The 5 chunks of red flesh he sells identify as something along the lines of "a delicacy for young bats"
When I handed one to one of the green con batlings it became my pet. Also, his merchant invetory refreshes, I bought a cople of the chunks of red flesh from him, and when I went to leave I stopped by him and he had 5 again.
The batlings follow you about like an enchanter pet, and can't (as far as I know) get inside the keep proper with you when you click on the door.
if you get attacked and you have a bitten victim or a confused mutation they would attack the mob that attacked you, you just couldnt make it attack or back it off.
once clicked, he sells red wine(infinite amount) and a chunk of red flesh(no drop and only 5 were available for a bit more then 9 plat) will assume its for the quest to get redfang back