I'd only put Vader on Patrol Leader making it a "Doom Decimator"

PL+RC+DV=46 points - still a bit costly IMHO.

Don't you mean a Decivader?

Vader on a Decimator would serve a slightly different purpose than when he is placed on a Shuttle. The DoomShuttle is usually cheap enough, and maneuvers poorly enough, that you use Vader at every opportunity because once things are no longer in the shuttle's sights it may be done anyway. With the Decimator you can be far more selective about using Vader because you almost certainly will get shots at anyone who can shoot at you and also because the Decimator is so many more points that you really can't afford to suicide it.