Need to use em_monitor or some other user for monitoring credentials in OEM 12c

We have been using APPS for monitoring credentials in OEM 12c with AMP.   But you have to manually change those if you need to change the apps password.  We would like to use something less powerful for monitoring and something that remains unchanged (if apps needs to change).  

I tried to use em_monitor  - but it never made the connection.  I removed the Apps user name and password (which works) and then inserted the em_monitor user name and password.   It was not able to conect.   

Just to be sure - i built a named credential for Oracle EBS and Database monitoring credential and it tested fine.