In the Army, are numbers pronounced “eleven” or “one-one” for PRT purposes?

Personally, as long as the message is being sent, received, and understood....

Single digits are preferable because thirty sounds too much like thirteen, forty like fourteen, etc. Imagine bracketing indirect fire support and saying "west sixteen" and in all the confusion they hear "west sixty" -- which by coincidence happens to be your exact location. So use a consistent format, radio or otherwise, and cut down on all the confusion.

I only heard/said "1-___", "2-___", "3-___", etc. Only exception I myself used was when counting reps as a PT test grader; insofar as I can recall. While I am not sure if its just an Army "norm" or rule to preface the 1st digit followed by the 2nd in most if not all situations, I would think it's a good way to reinforce the habit regardless. If that's wrong, well, there are bigger wrongs in the world to worry about than that. No need to over-think it; you'll be fine.