Way back in the RM2 days there were a number of RM campaign settings, Ancient Greek, Ancient Egypt, Pirates, etc.. They did a great job of first describing the culture and assumptions of the setting, then laying out how they worked in RoleMaster terms. There was never a problem with being limited due to the RM rules set, because they tweaked the rules where necessary in order to fit the setting (new races, new magic, etc.).
If you keep in mind Setting First, Rules Second, I think any campaign setting could be adapted to RM, that's one of the strengths of such a flexible system.