I think that's right, the FIFA rule says a player can only be registered with 2 clubs a season - nothing at all about how many they can play for, just how many they can be registered with. And a loan doesn't affect a players registration.
"They thought they had signed striker Alex Revell from Southend United only to be told by the Football League that they can’t because he has already represented two clubs this season" from the Bucks Free Press looks like Revell is going back to Southend whther he likes it or not