Is it really against the rules for an OCSM to be a mod?
It would be considered a conflict of interest. It might lead to speculation about how objective you can be in the case of someone saying things against you as a model. Or people might think that you're biased if you moderate a dispute between a regular member and another OCSM. I'm not saying you would actually do that, but that's the reason why Freeones doesn't let OCSMs be moderators.