We have wolves and Wargs, and Werewolves who are actually spirits in wolf form, and traditional werewolves -- which the original poster was asking for.
It's all a bit confusing.
Considering Tolkien's affinity with northern myths, I'm sure he held the wolf in high regard. Also taking into account the etymology of 'Warg' (check the Faroese in the signature
) it seems fair to say that Wargs and wolves are not separate things.
There are no documented traditional werewolves: whether involving changing shape at the full moon or utilising a magic wolf-hide.
There are particular and generally potent spirits who are placed into the Warg form. See
The Silmarillion.
So, two groups.
But, as has been pointed out by Tuor, the tale of Beorn should give anyone enough scope to write about a traditional werewolf in Middle-earth.
