When you say he gets no bites, is his profile not getting viewed? Is he not getting messages? Or is he messaging women and not getting replies?
For the record, I've only had two women ever message me on OKC... and a good 99% of the ones I've messaged never replied. This is long before I'd ever heard of or considered poly... so I'd look at other things first.
You reviewing his profile and trying to pretend you're neutral could be a good help. Or look at other guys' profiles and see what gets your attention, then try to get his profile to have similar things.
Online dating can be tricky because people are afraid of stalkers/creepers, plus people tend to hold onto higher standards.
That said, I know people who have success with OKC... so I wouldn't give up on it. It's probably a good option, but you need to learn the ins and outs...