I don't know. But I do think that he would be in there. Maybe they are not finish with his character design. Most likely all of the character that are not dead may be come back in MGS4. Here is what Kojima has stated:
CVG: In MGS 4 we see the return of Raiden, Liquid Snake and Ocelot. Can you tell us about the plot which combines all these familiar characters?
Kojima: In MGS 4, the only character you will be able to play as will be Snake. In the story, I'd like to include all the characters from the whole series if the story allows it. I would like to have a big wrap up in MGS 4 which explains why the characters acted in the way they did in previous games, so everything can be finally revealed in MGS 4.
There is more to the interview.