So, are the events of "The Suicide Squad" now considered canon to the new DCU? If that's the case, wouldn't that make it the first official DCU film as well?
Not exactly. Certain events in
TSS, such as the scene where we learn that Bloodsport sent Superman to the hospital with a kryptonite bullet, are actually not canon. (FYI, Gunn clarified this detail about Bloodsport during one of the press junkets for
Superman.) However, it goes without saying that
many other events from the film (e.g., Project Starfish, Rick Flag Jr.'s death at the hands of Peacemaker) do, indeed, carry over into the DCU.
I suppose you could call
TSS vaguely canon. I would definitely recommend it to anyone hoping for a more complete experience with
Peacemaker, and, to a lesser extent,
Superman, which features a cameo from at least one significant
TSS character, namely Flo Crawley. Just try to keep in mind that, technically speaking, nothing is officially canon until it's referenced in the new continuity.