I think this must have been changed in later versions of BGT. I fought this beast yesterday. Was amazed at how quickly he regenerated. Had him at Near Death and Badly Injured several times, and suddenly he was Uninjured or Barely Injured. However, we hit him with much else than just the silver weapons. I spawned some ogres with a wand, and I saw they hit him with ~30 damage multiple times during the fight. At some point I equipped our tank Kagain with the dagger we found somewhere, but I'm sure he hit him before too, with a +2 weapon. What finally did him in was when we all could focus on him (all others dead), and Imoen and Kivan hit him with +2 arrows, and some of the previous acid strikes (spell) helped too, plus Viconia with a +2 hammer, and yet more Magic Missile salvos.

Epic fight, but it looks like +2 weapons can deal damage to him in today's BGT.

This is not true, those flag can be set and used in the BG2 engine. As a matter of fact, the greater wolfwere requires silver weapons in both Tutu and BG:EE, but not on BGT (this is by design and not because it is impossible).

The greater wolfwere behaves differently in the different versions of the game:

In BG1 vanilla and BG:EE it requires silver weapons and regenerates 5 HP per second.

In Tutu it requires silver weapons and regenerates 2 HP per second.

In BGT it requires just plain magical weapons and regenerates 6 HP per second.

I know they are there, and can be set, but I wasn't aware they were actually used in the BG2 engine. I'll take your word for it.

Interesting that there are so many variants of this particular enemy in the different game versions. Despite the even higher regeneration in BGT, being able to hit him with any magical weapon (even +1?) should make the fight easier -- but then I guess being only able to hit him with a select few weapons was pushing the envelope a bit.

Yes, in BGT any magical weapon works, even +1.

I'm personally using Tutu, but I modded myself the regeneration rate back to the vanilla value, i.e. 5 HP per second.

It doesn't bother me that you must use silver weapons, because I know which and where they are. Besides, you can also use other means to deal damage like spells (the gretaer wolfwere has 50 % elemental resistance, but 0% magical one, so for example magic missiles do full damage) or items (e.g. Potion of Firebreath, etc.).