You can straight use any RM2 profession with RMC, just keep in mind that they're not subject to the same balance factors, so they may throw your game out of whack.
I personally find the Semi costs for spells and PPD to be steep enough that unless you're fudging SLA it's rather hard to develop loads of spells and enough PP to power them. (Semis all pretty much suffer from a generally slow progression due to straddling the middle.)
Played to core, generally none of the RM2 semis will be game breaking. . .start adding in options, like "10% Activity Instant Spells" from Spell Law, and some of them, like the Warrior Mage and Witch Hunter start to get signifigantly more powerful (enough to unbalance a game if you're not paying enough attention.).
There is an Essence based semi in the Combat companion also. . .Tim did one semi for each realm in that book. . . .The Essence one could be used in place of the Warrior Mage.