AES does not "monitor nodes". Nodes send data to AES.
The connection string inside the node record is used when AES tries to contact a node based either on a user action (in the Enterprise landing page) or to get information to investigate an issue that was sent to AES by the node.
If you do not see alerts, exceptions or health status from a node in AES, start the trouble-shooting on the node itself.
If a node is sending data to AES, but you can not "soap" to the node from AES, bring up the node in enterprise health, bring up the requestors tab, enable tracer then press search. Tracer / logs should show what's happening with the call from AES to the node.