In a hospital environment CNM's are as you say a Physician Assistant.
I believe that many CNM's operate within an autonomous framework in hospitals. Don't forget that CNM's are treating only low risk women. Once it steps outside the role of low risk a physician collaboration occurs. Many CNM's have hospital privileges and attend planned hospital births or transfer form birth center births. I think CNM's might take issue with being portrayed as PA's... they are very independent and I have attended many deliveries with them out of and in hospitals.
What was it about the interaction you saw with the CNM and the MD's that made you feel their roles were restricted. Is it just your particular environment?
Just interested because I may be a future CNM
Carolyn