Yes sir, as I am aware that only a gov4 makes it possible to build lvl4 regional MICs I have been thorough in building these, good that you ask though as I am sure many are confused by this, as I were myself, when first playing a Swêboz campaign.
And even though Eburonum is the only of the listed settlements in which to recruit germanic mercenary generals the others feature celtic lesser kings who function in a similar manner ie. as mercenary generals.