Denominations are not.
So someone can belong to a denomination, have membership in it, and not be saved.
And people can be saved by faith in Christ and not belong to any denomination at all.
So don't buy into the Catholic meme that if you belong to a church, you are saved.
That is not taught at all in the NT.
I understand your point that if he's not really saved, then he's not a legitimate Baptist minister. Sad to say, he probably could be credentialed if he gave all the right answers even though he wasn't saved. Wolves in sheep's clothing comes to mind.
In Southern Baptist churches you cannot “join” unless you are professing faith in Christ as Lord. I don’t know about other denominations. Perhaps they do things differently. I think the Presbyterian reformed way is to assume you are until you prove you’re not, or something like that. Not trying to misrepresent anyone’s denomination here, so anyone reading this don’t jump on me. Just guessing, but I do know that one cannot join an SBC — i.e. become a member — unless one professes at the same time — faith in Christ as Lord — or by letter from another SBC church (which would be the same thing since one could not have joined THAT church unless following the same process).