Tuff one.....
First, I do not know the wreck in question, so this is a general consideration.
If I, as guide, was to lead a dive into something -- be that cavern/cave/wreck -- I would want to ensure that the divers had the appropriate skills. Since this is not an instructional situation (and since I am *not* a cavern/cave/wreck instructor), we'd essentially be diving as a team -- and in these environments, you have to feel confident about your team. So if there was a diver, whom I didn't feel good about and whom I did not feel would have the appropriate skillset for the team, I would not make the dive with him, regardless of who he is or what plastic he carries. It's as simple as that.
Was the guide right in refusing the cave-diver? I dunno. I'd have to go dive the wreck and go dive with the cave-diver to answer that. I've seen some cavers, who'd possess worse bouyancy-skills than my OW-students, so I almost never take a card as "final proof" of anything. (Although the bulk of cavers are "spot on") And I have seen some wrecks, which hardly qualify as "overheads" too.