Since Cleric is our only prolonged exposure to an erratic, and assuming that he is semi-indicative of others, then I'd say the Consult Nonmen might actually be pretty good at combat. Cleric was crazy as fuck but he seemed to get his act together pretty quick when shit got real. And he wasn't just rampaging per se, at least not every time - he actually used tactics and coordinated with Akka against Wutteat, for example.
Even the Ishterebinth courtiers seemed at least as lucid as Cleric, if not moreso. So I can envision the Consult's ranks of Nonmen being effective so long as it's in relatively short bursts, and assuming they have a good book with them (heh). And that's disregarding any possible restorative aid via Tekne.