Well, not really a loophole, but this is very interesting.
From the AP news on the Rincon story:
"For right-hander Scott Baker, brought up from Triple-A Rochester to fill Rincon's roster spot, this wasn't the way he envisioned making his major league debut."
A team gets to replace on their roster (active not 40 man) any player suspended for illegal susbstances (I have confirmed this as 100% true). Fight related and other suspensions - the team plays short. So the union gets another job (and MLB salary - albeit short term).
I wonder what the thinking was in making that exception - possibly that a team is going to have multpile participants tested all at once. And if you have 5 positives and suspensions that would be too severe? And how would you decide who to stagger?
I guess it is a minor point considering where we are coming from. Still an interesting observation.