Yes, former players on rivals can become friends. Especially if they moved on to the NFL and played together. Warren Sapp and Derrick Brooks are friends, played together, won a SB together. They can certainly support one another. Even publicly.
Now, to be fair, these same players have been vocal in their support of the program. Johnson has been a donor, enough to name the locker room after him. That’s a multi-million dollar donation. Irvin is always repping Miami. Sapp, too, but no one asks him unless he‘s on the Rich Eisen Show.
But wearing another school’s gear is over the line, especially one in direct competition with high school recruits and portal talent.