Happyface888,
That means then, there is Marine Ich in your marine system and all fishes are infected.
The implication to your question is that you may be considering to do nothing about it. Yet, the right thing to do is remove all fish and treat them. The concept of seeing if the fish will 'ride it out' is similar to waiting to see if grandma will recover from pneumonia on her own.
I don't decide what fish to treat based upon their resistance to disease. Keep in mind I wrote in generalities before. Every individual fish has it own tolerances to diseases and water quality and environment and tank mates, etc., etc. So what may be true for a group of fishes may not have any bearing on the one fish in captivity.