[Huinesoron]

Most definitely! The Silmarillion tells us as much:

Originally Posted by Silm: Valaquenta

...in ages forgotten he contended with Manwë and all the Valar, and through long years in Arda held dominion over most of the lands of the Earth. But he was not alone. For of the Maiar many were drawn to his splendour in the days of his greatness, and remained in that allegiance down into his darkness; and others he corrupted afterwards to his service with lies and treacherous gifts.

We know for certain, because the text directly tells us, that Sauron was one of those Maiar (accounted the greatest 'among those of his servants that have names'), and that the Balrogs were too. Osse, for a time, would have to be included, though he repented.

As to the others, the werewolves, vampires, and dragons... were they Maiar? Many have theorised as much, but I don't think Tolkien quite says. 'Werewolf' could simply mean 'Warg' (the goblins of the Third Age could speak to Wargs, so why not Beren and Luthien?), and the text doesn't actually say vampires are anything other than giant bats. Dragons were explicitly machines in the very early Legendarium; who knows what Tolkien thought of them later?

I believe Ungoliant is a Maia in at least one telling of the story; and in the late Legendarium, Tolkien toyed with the idea of some Orcs being Maiar!

Originally Posted by HoME X: Myths Transformed

For Morgoth had many servants, the oldest and most potent of whom were immortal, belonging indeed in their beginning to the Maiar; and these evil spirits like their Master could take on visible forms. Those whose business it was to direct the Orcs often took Orkish shapes, though they were greater and more terrible. Thus it was that the histories speak of Great Orcs or Orc-captains who were not slain, and who reappeared in battle through years far longer than the span of the lives of Men.*

*Boldog, for instance, is a name that occurs many times in the tales of the War. But it is possible that Boldog was not a personal name, and either a title, or else the name of a kind of creature: the Orc-formed Maiar, only less formidable than the Balrogs.

Originally Posted by HoME X: Myths Transformed

In any case is it likely or possible that even the least of the Maiar would become Orcs? Yes: both outside Arda and in it, before the fall of Utumno. Melkor had corrupted many spirits - some great, as Sauron, or less so, as Balrogs. The least could have been primitive (and much more powerful and perilous) Orcs; but by practising when embodied procreation they would (cf. Melian) [become] more and more earthbound, unable to return to spirit-state (even demon-form), until released by death (killing), and they would dwindle in force. When released they would, of course, like Sauron, be 'damned': i.e. reduced to impotence, infinitely recessive: still hating but unable more and more to make it effective physically (or would not a very dwindled dead Orc-state be a poltergeist?).

On this last point, however, Tolkien wavered considerably - almost in the same essay, Orcs were seen as Men, Elves, animals, constructs, or Maiar. Elves is the one that stuck, because it's in the Silm.

Other Maiar of Melkor had less physical form:

Originally Posted by HoME X: Myths Transformed

But it is known that Melkor had become aware of the Quendi before the Valar began their war against him, and the joy of the Elves in Middle-earth had already been darkened by shadows of fear. Dreadful shapes had begun to haunt the borders of their dwellings, and some of their people vanished into the darkness and were heard of no more. Some of these things may have been phantoms and delusions; but some were, no doubt, shapes taken by the servants of Melkor, mocking and degrading the very forms of the Children. For Melkor had in his service great numbers of the Maiar, who had the power, as had their Master, of taking visible and tangible shape in Arda.

hS