Wow, I should check in here more often. Using the silver or non-cold iron flags is a bad, bad idea. Only seven weapons (three in SoA) are flagged as non-cold iron, as it is a deprecated flag from BG1. The silver flag is in essentially the same boat.
Werewolves are vulnerable to magical or regular silver weapons. Unfortunately, if you flag a monster with these immunities, the engine stacks them--making them vulnerable to only magical silver weapons. The same applies to wolfweres and their non-cold iron immunities.
Greater werewolves do not get higher weapons immunities--it's a strict magical/non-magical delineation.
Littiz, do what you think is the best and the only imperative should be not to unbalance game. After many debates, many questions, with experimented AD&D players, many searchings, I reached the next conclusion : no one can say - being absolutely sure - how a true AD&D Greater Werewolf should be. What CamDawg said above is certain only for normal werewolves, not for greater ones. And neither BG2 developers didn't follow strictly the rules, so why would you do it ? Point.
