What is the Collective noun for registered nurses?

Answer 1

There is no standard collective noun for a group of nurses, in which case any noun that suits the situation can function as a collective noun; for example, a group of nurses, an army of nurses, a team of nurses, etc.

Answer 2

There is no standard collective noun for a group of 'registered nurses'.

Collective nouns are an informal part of language. Any noun that suits the context can function as a collective noun.

I have no doubt that, where there are groups of registered nurses, a number of collective nouns have been created, for example, a grumble of RNs, an injection of RNs, a comfort of RNs, etc.