Should they skip Raditz? Yes and No. Heres my explanation, if Piccolo is going to reveal to Goku that he is not from planet Earth and is in fact from another planet ( Planet Vegeta) then the character of Raditz becomes absolute. Even though Raditz's part has become absoulte that doesn't necessarily mean that they need to completely wipe out the character. What I think should happen is they should instead add Raditz to the Vegeta & Nappa crew. That way you can have Nappa killed by a last attempt of heroism from Piccolo ( I know I'm changing the story a bit, but expect changes for the sequel and it also doesn't completely undermine the ability/strength of the other characters in Dragonball , something the manga did to great characters such as Piccolo, Tien etc :: Which kind of bothered me because I found them to be such great warriors:
. Then once Goku arrives from otherworld, Vegeta and Raditz would be the ones that he has to defeat. Having Raditz at this point in the film would help have a complex situation where Raditz is torn between his allegiance to Frieza and Vegeta and having to kill his brother. It would make for great dramatic sequences in the film. So in a way I'd have Raditz take over Nappa's part, When Vegeta orders Raditz to kill his brother and Raditz refuses we can have Vegeta terminate/kill Raditz in the same fashion he killed Nappa in the anime/manga.
Will they skip Raditz? Who Knows