BryanKMorrow, I suppose it depends on how popular you expect the Marketplace to become.
A thread for popular probes might be a good start, but a single thread can quickly become very confusing to follow if multiple probes are being discussed.
Ideally, a section within the community that can be linked to directly (maybe a sub-category of CA Unified Infrastructure Management (f/k/a Nimsoft Monitor)) would be nice. This would allow a link to be placed on every probe in the marketplace to easily direct users questions/feedback to a central location.
Tagging posts may work, but since tags can be created on the fly by any user, it can be difficult to ensure you capture all discussions with a tag filter. If it is possible to place permalink to a "marketplace probes" tag on the Marketplace, it could be a workable model. I think posting the link on the "Support Model" line of the custom probes that are Community supported could work.