pretty much this... late game grens are cannon fodder, no matter the veterancy. since they are decent in early game (when allied vet is not yet a factor), the only imaginable buffs would have to be to their late vet (2, probably 3 though). with almost all stock infantry of the allied factions outperforming grens by a big margin, and ostheer generally having problems to wipe units effectively, i doubt that a vet 3 buff to grens would do a lot of harm, especially if it's not too strong.
But then yet again Elite Troops