Baneblades? maybe, if one could bribe/steal/scavenge one. But not a forge world, remember that the imperium wants its worlds and hardware for itselves. Rogue traders are not meant to own things the empire need, the yare meant to go beyond the borders of the imperium. If the rogue trader has something extremely desireable to the empire, then make no mistake, the empire will try to take it, and the empire will succeed.
So no titans.
Then again, its your game, you can play it however you like.