Magic per se doesn't really exist in Middle Earth. What some races perceive as magic (elven cloaks, the ring, nifty stuff Gandalf did, Sauron's big cloud cover for his armies) is all just a deeper understanding of how the world works and the application of that knowledge.

So, the Valar could teach someone how to do things that others would find "magical", but that is about it really. In fact i believe they did this early on, before Morgoth really screwed everything up and they decided strict non-interference was the way to go.

This is also basically what Sauron was doing when he instructed the elves in ringlore.

So basically, they probably could, but after the very early first age they wouldn't.

It sounds like your asking if you could use D&D style clerics in a Middle Earth game, and no, I don't think that would fit.