The producer for A:EMH noted that the show was originally supposed to share continuity with WOLVERINE AND THE X-MEN, at least circa season two. However, when W&TXM ended up not getting a second season, that threw that equation out of whack. Thus, I imagine some promotional artwork for some X-Men could have been made for A:EMH, and a cameo or even guest appearance isn't out of the question.
In recent years, the X-Men have actually proven fortunate in terms of getting their own TV shows; roughly as much so as Spider-Man. The 90's had "X-MEN", and the first decade of the 21st century (2000-2010) had "X-MEN EVOLUTION" and "WOLVERINE AND THE X-MEN", in addition to the drafting of the "X-MEN ANIME" and "WOLVERINE ANIME" from Madhouse in Japan, which is airing now. In comparison, the Hulk has had only two cartoon shows since the 80's.
However, the X-Men have been featured in other Marvel series before.
In the 1966 era "MARVEL SUPERHEROES SHOW", which featured Xerox animated tales of Thor, Captain America, Hulk, and Namor The Sub-Mariner, the original X-Men were featured in one of the Namor episodes. It was not a very good outing.
Magneto was the villain in the 2nd episode of the 1978 "FANTASTIC FOUR" cartoon, the one that infamously replaced Human Torch with HERBIE The Robot. It was not a stellar outing. The episode was naturally titled, "The Menace of Magneto".
In the 1981 "SPIDER-MAN" series that aired in syndication - the series that impressed NBC enough to warrant "SPIDER-MAN AND HIS AMAZING FRIENDS" - Magneto also was featured as the villain in his own episode, "When Magneto Speaks, People Listen". Again, he was featured as a standard villain. This was the series' 6th episode.
The X-Men appeared more in "SPIDER-MAN AND HIS AMAZING FRIENDS", especially because both of the "amazing friends", Iceman and Firestar, were mutants and former members of the team. The second season in 1982 featured only 3 original episodes, which detailed the origin of the three characters. The X-Men appear in flashback in "The Origin Of Iceman" but are featured more heavily in "A Firestar Is Born". In that episode, Professor X, Cyclops, Angel, Storm, and Wolverine are all featured and given speaking roles; the villain of the piece is the Juggernaut, sporting his original pants-less design. Storm and Wolverine were considered "new members" and Wolvie had an infamous Aussie accent (and put up a poor showing against Juggernaut). Interestingly, NBC considered his claws too violent, and he never really appeared much with the X-Men again.
The 3rd season of "SPIDER-MAN & HIS AMAZING FRIENDS" in 1983 had 8 episodes, and the X-Men were featured twice. They had a small cameo role in "The Education Of A Superhero", which featured the third appearance of Videoman (which had no relation to his two prior appearances). This new Videoman was good, and sent to the X-Men for training. The X-Men only appear in the final scene, but the roster is Prof. X, Cyclops, Marvel Girl, Wolverine, Storm, Nightcrawler, and Colossus. None of them speak. However, the second-to-last episode of the season/series, "The X-Men Adventure", naturally featured the entire team. The plot was structured so that every member of the X-Men got a few lines and a chance to show their power - a back-door pilot if there ever was one. The X-Men this time were Prof. X, Cyclops, Storm, Nightcrawler, Colossus, Sprite (Kitty Pryde), and Thunderbird. Sprite was actually Kitty's codename before she went with Shadowcat. This was Thunderbird's only animated appearance, although his powers were wrong - he could stereotypically transform into animals here. The episode focused on Firestar mostly, and on surviving an X-Mansion turned against everyone. NBC didn't bite on an X-Men series, but Marvel did produce a pilot in 1989 which became known as "PRYDE OF THE X-MEN".
While the X-Men had their own cartoon series from 1992-1997, they did appear in other shows of the time. The entire team from their own show appeared in two episodes of "SPIDER-MAN: THE ANIMATED SERIES"' second season in 1995 - "The Mutant Agenda" and "The Mutant's Revenge". While FoxKids flew the entire Canadian voice cast to L.A. to record these episodes (which, at the time was considered an expense), Wolverine and Beast were essentially the X-Men who got the most airtime for these episodes. Rogue did get to flirt with Spider-Man a couple of times, although some coloring errors marred Cyclops' appearances. This episode is best remembered for Spider-Man's brilliant retort to Storm's over-the-top screeching.
STORM: "Power of light-ening! STRIKE AGAIN!"
SPIDER-MAN: "Um...power of web-shooters! Get REAL STICKY!"
It also featured the Hobgoblin, as voiced by Mark Hamill. The only dilemma is that Hobgoblin vacated the two-parter and instead Spidey and the X-Men were left to fight a fairly generic monster, which kind of sucked. However, before "MARVEL SUPER HERO SQUAD", this was the first and last time Spider-Man and Wolverine teamed up on a cartoon show.
By the final season of "SPIDER-MAN" in 1997-1998, the show devoted 3 episodes to do a loose adaptation of the SECRET WARS plot from the comics, in which Beyonder zapped Spider-Man to another planet with a team of villains to study the nature of evil, and Spidey chose which heroes to recruit for his side. He remembered the X-Men, but decided on Storm because he figured she was the most powerful. In "real life", the voice actress who played Storm for the first few episodes of the X-MEN show lived in L.A., so rather than pay to ship over Canadian actors again (since by 1996-1997 Marvel was in the red), the writers only included Storm for logistic reasons. Thus, Storm got to tag-team with Spider-Man, the Fantastic Four, Iron Man, Capt. America, Black Cat and Lizard (!) from episodes #61-63: "Arrival", "Gauntlet Of The Red Skull" and "Doom".
The X-Men also have some cameos in the 2nd season of the "FANTASTIC FOUR" cartoon from 1995-1996. In "Prey Of The Black Panther", Storm and and her adopted son Mjnari (made for the 90's series) have a background cameo. In "Nightmare In Green", several of the X-Men are seen on a rooftop observatory in their civilian attire - Cyclops, Jean Grey, Gambit, Wolverine, and Storm. The Juggernaut is also seen climbing out of the ocean, as a reference to "X-MEN" Season 3 episode, "The Juggernaut Returns", which also aired in '95. The Blackbird jet is also seen flying about during the '96 series finale, "Doomsday".
The X-Men also guest starred in an episode of the motion-comic style "BLACK PANTHER" series which was made in 2006 but wasn't released in the U.S. until recently.
Hope that was a nice retrospective for everyone.
