No health monitors on GTM pool or servers, but status still "availble". How?

I think I may have found the answer. In this case, stopping the NTP service on one of the servers resulted in it going unavailable/red in the GTM. This seems to indicate that the GTM is indeed making a connection to port 123 to the server. Additionally, with the NTP service still stopped on the server, I added a Gateway ICMP monitor to the server object in the GTM. While I could ping the server, the object was still red/unviable. This must suggest that as long as the port 123 connection was failing, any other monitors were not even considered.

I spend most of my time in LTM so I am always trying make comparisons between GTM and LTM. In LTM when you add a node (server), LTM automatically assigns an ICMP ping monitor to the object. If that doesn't succeed, then the object is always red. But in GTM, the base/default monitor for the object must be the service port you assign to it. So the GTM is quite different in that regard.

Anyhow, going back to GTM, I am now thinking that all new server objects should be added with the * service port, then use a port-specific health monitor.