I'm not sure there are any rules about contacting current players? I mean, Kiffin is potentially friends with all of his former team at Ole Miss. Why can't one friend text another friend?
Trying to make a rule against something like that, would be kind of silly and I'm pretty sure would get thrown out of any court in the country.
And anyway, it's all done through agents now anyway. Arms-length comms and whatnot.
But even so, yeah, giving your current interim head coach the opportunity to advocate for LSU instead of the school he's actually coaching for, is, well, really dumb.