If a potential faculty presenter was previously employed by an ACCME-defined commercial interest, are they ineligible from participating in our ACCME-accredited activity?

Not necessarily.  The financial relationship of the individual should be from when the individual was in control of content and 12 months prior.  If the faculty was not employed by a commercial interest during his involvement in the CME activity, then his employment is not relevant but would need to be disclosed to learners.  If on the other hand, he was employed by a commercial interest during his involvement in the CME activity, then he is prohibited from serving as faculty except under the 3 special-use cases.