rotorblades, as far as I am aware, any aircraft entering a CTAF(R) must monitor the frequency regardless, a call to ATS to advise "monitoring" would just be a waste of time and further clutter up the radio with more wasted calls just like "at time", "we are" etc..
KS is correct when he questions giving up a level of protection. Why would any RPT want to reduce its traffic info. in the CTAF? Not me, and I am sure that my company would not support it. And I don't think the magistrate would agree with a decision to reduce your traffic info. when inquiring into an incident that was traffic related.
Pilots don't usually ignore ATS calls on purpose, but sometimes high workloads in the CTAF will place a reply to ATS as a lower priority.
If an aircraft does not respond to ATS within the time limit then ATS must assume a problem has occured and start the SAR procedure.
+G