Ok, so its not quite as bad as I thought. After researching a little deeper-- I figured out partially what my problem was. In order to get the Minibrute arp to sync properly, the arpeggio must already be on and running, then a Midi start+clock will initiate sync. When sync is initiated in this order-- the Minibrute syncs up really well I'm finding (!) It doesn't seem to drift like some other Midi arpeggio syncs I've used.
I guess I'm always trying to 'play' the arpeggio to a drum machine, the way I would with an SH101, but the Minibrute simply doesn't work this way. Not a big deal for studio playing, but maybe not so great for playing live. It would be nice if it could sync up on the fly.
Probably if there was some hardware mod to inject external clock, this 'on the fly' style sync would be possible. Maybe someone has already published this modification. I think I'll take a look.