I don't think "an entirely different ethical framework" should apply when you're "treating someone versus learning to treat them." First of all, "learning to treat someone" is not clearly separable from treating them. That's the whole point of medical residency-- you spend a bunch of time watching and helping doctors treat people, so that you can become one yourself. Ethical standards don't radically shift the moment a resident enters the room.

The concept is absurd. "Whoa guys! A resident just entered the room! Now we have to fill out all our forms in pen rather than pencil because the ethical standards just radically shifted! Now we're learning how to treat rather than treating!"

I think you are also missing one of the big points here, which is that the study protocol was exactly the same as what the doctors were doing anyway. So philosophical tangents like whether risks should be minimized more in research or treatment are irrelevant in this particular case. The risks are the same because the protocol is the same.