im gonna say no because the emphasis of the game is singleplayer and honestly the mp seems tacked on, despite what they claim. it's not a COD so don't hope for a lot MP-wise is all i'm saying
it's like asking fallout 3 to have an MP beta... its just silly

Usually the only reason I know of, why a developer/publisher won't release a beta, is because it builds hype/anticipation (that's why there hasn't been a Call of Duty beta in 2 frickin' years..) and since then the game has either had problems of some kind. MW2 was full of glitches (however I believe that's due to IW wanting to sabotage the final game Jason West and Vince Zampella made) and Black Ops suffers from lack of originality.

So a Rage beta sounds very good, since it's a first go at a multiplayer like this for id Software.