The key to manage Sun/Linux flavors is net-snmp. If you search the forum from net-snmp you'll see people have had a lot of different issues monitoring these types of servers because of the net-snmp version they used. I think some versions are better than others.
Assuming net-snmp is right then you can monitor anything that's in the SNMP MIB. Out of the box cpu, memory, drive space is available and then you can build custom pollers for anything else. I think the content exchange area has a few pollers already built.
After the polling is done you can create alerts based on the thresholds you want.
Pretty cool stuff omar.