[Inziladun]

Originally Posted by TheLostPilgrim

In The Silmarillion, we have Werewolves, Vampires, and other more "High Fantasy" creatures working as the beasts of Morgoth and later Sauron....But what about in the time of the Lord of the Rings? Did Werewolves and Vampires still exist in Sauron's armies, and we were just not told of them?

That sort of creature could have been among the "older, fouler things than Orcs" that Gandalf mentioned, out of sight and knowledge for the majority of Middle-earth's people. Sauron's forces were numerous enough, I think, to have included such servants without their being generally known.

For werewolves, we have the Wargs as a close approximation (apparently hyper-aware wolves actively serving Sauron).

Originally Posted by TheLostPilgrim

Also, if Smaug had not been killed years before, would he have fought for Sauron--or would Smaug have perhaps acted as his own agent, seeking power for himself and wrecking havoc in his own way--basically acting as an independent yet also fearsome power?

Gandalf seems to have thought Smaug would have acted for Sauron, though whether he would have done so willingly is up in the air. In fact, that was given in Unfinished Tales as one of Gandalf's prime motives in helping Thorin retake Erebor.

"The dragon Sauron might use with terrible effect. Often I said to myself: 'I must find some means of dealing with Smaug.'"

The Quest of Erebor

Used implies possible underhandedness on Sauron's part, though I think it likely Smaug would have been amenable to placing himself at Sauron's service, especially given the promise of slaughter and plunder thereafter.