You can use either of them to manage the server. Both are connected to the BMC, but RMM4 has a dedicated physical NIC port. But remember not to configure the BMC channel 1 and the RMM4 in the same IP subnet. If you need only one management port, it's recommended to use the RMM4 port.
Ok, I think I only need one management port, so will use RMM4.
I don't know why you must require two differents ip to manage, surely I will set both port one for x.x.X.1 and other with x.x.Y.2