While we have yet to put anything in production, during our POC of Monitor Solution, we did a few "SNMP Get(s)" to monitor CPU and Memory utilization on a per LPAR basis.  So you can certainly expand on this approach.  There should be quite a bit you can get out of SNMP Gets.  

Trap receiving is a different story though.  We found, even with the correct MIBs loaded, we could rarely interpret the traps.

Another approach we are working on is "Remote Command".  This is a utility included in the connectivity tools for the AS/400 on Windows.  It allows you to run various commands within the AS/400 and return those results to your command window.  This is where we want to end up, but simply have not had the time.

Right now, we run a few scripts within the AS/400 to monitor for error states.  We want to continue to use those, but run them perhaps from "Remote Command"; or you can even use ODBC.