Benoit, you actually had a partial answer, everything you said was correct, but after next reboot, the account locked. After several hours of more research, the following issue was discovered, with the appropriate resolution.
Enterprise Manager had the default SYSMAN password stored for its credentials, and was trying to lock in with that password in rapid succession (300 times a minute or so according to the Event Log). Hence, after several rapid tries with the same wrong password, Oracle locks the account.
Setting a new password in SQL*PLUS or SQL Developer doesn't reset the password used to login to Enterprise Manager, to reset the password in enterprise manager, you need to open a command prompt and do the following:
emctl config oms sso -remove
emctl stop oms
emctl start oms
During the above commands, it'll prompt you for the current SYSMAN password, which you can enter, and it should remove the SYSMAN password used by your Enterprise Manager Console, replacing it with the one you just entered.
"Logon Per Sec" and "Logon Per Tx" can be found in OEM REPOSITORY (e.g. look in sysman.mgmt$metrics_daily view, the metric_name = 'instance_throughput' and metric_column like 'logons%'). The other metric will also be there, these are maintained in OEM REPO not in individual targets.
Best Answer
Yes, we can view the listener status from OEM (Oracle Enterprise Manager). I am uploading the two screen shot related to listener in Oracle 11g,OEM(Oracle Enterprise Manager) status.
and the current 'Up Status' of Listener.
Note: I have highlighted some part due to security reason.