I think there are a lot of interesting discussion concepts badly intertwined in this thread. In terms of teaching, I think it's silly to worry about a person's station. If someone knows more than you, then they can be your teacher. So a PA or NP with years of experience ought to be able to teach a resident fresh out of med school. The student will absolutely surpass the teacher in this situation given the ultimate position the resident will achieve, but until that happens, there isn't a good reason a mid-level ancillary professional couldn't teach a higher level professional in training. Heck, an attending can learn from an intern if the intern knows more about a certain topic or procedure. It's substance over form.
As for NP/PAs "stealing" procedures, this happens a lot at hospitals where you have to do a number of supervised procedures before you are "signed off" to do them. In a hospital with a residency program, I think the resident, the person the government is effectively paying the hospital to train, needs to get first crack at it.
I agree that the resident should get the first crack. The issue I see (although infrequently where I am) is that some attendings are not into the teaching aspect. They want to get done and will give procedure to an NP/PA who has done a bunch and can do them fast rather than take the time to teach the resident (or let them get practice). It goes along with what Tired is talking about. The attendings don't want to do their primary job which is instructing residents.
Finally, the basic concept of NPs/PAs acting autonomously are being marketed to patients as the equivalent of physicians represents a huge misstep by the medical profession. Physicians need to organize and lobby to set limits as to what ancillary professions should be allowed to do and not do. There is huge encroachment going on, there are ancillary professionals acting as if they are physicians, some even holding themselves out as doctors. In law, similar encroachments have been attempted by paralegals, realtors, accountants. In each case lawyers fought tooth and nail and very specific legislative boundaries as to what constitutes "the unauthorized practice of law" now exist, into which ancillary professionals dare not treat or risk huge lawsuits and penalties. Physicians could do likewise, but thus far are poorly organized and their organizations even more poorly funded. This needs to be fixed, or you will see gradual erosion and blurring of physician roles, additional encroachment, and more and more non-med school trained individuals calling themselves "doctor". The high costs of healthcare make these ancillary professionals an easy fix in the government's eyes, so doctors actually need to move fast to shut this down.