Ah, this guy mentions he had to reset the card before he could get it going:
http://xorl.wordpress.com/2011/08/21/ibm-rsa-ii-card-replacement-and-re-configuration/
Yup, I remember I had to do that to if things were messed up. Let me know if you get that bloody card fixed.
Concerning your question (sorry for other readers for being Proxmox off-topic)
The baseboard management controller BMC is integrated on the motherboard and available even when no RSAII is installed and monitors base system health but can do less and is less that easily accessible.
It can be accessed over IPMI tools if I remember right, Windows required some extra bridge tool. Basically it allows you to get some sensor data and remotely control power of the server, and that's mostly about it.
I don't remember if RSAII cards extend BMC or if it overrides it once the RSAII is installed.
Difference is also that the BMC port is shared with one of the onboard NIC ports, RSA has its dedicated port.
RSAII can do much more (KVM, remote media, mail-warning, LDAP auth, etc...) compared to the base BMC, but it costs extra money.
On the later systems IMM needed a physical key to enable all features, I have some M4 systems withe IMM2 (all onboard) which enables features using activation keys just like HP's ILO
Also IMM(2) is way, way better than the ol' RSA's, at least IBM learned a bit out of the past :-\
