For sure a NIL-payor can require exclusivity. Nike isn't paying a player who then signs a deal with Reebok (you know, in an alternate reality where players are being paid to promote something).

But it is a little silly for RBC or CougConnect to require exclusivity between eachother. If one REALLY DOES have a promotion going with a restaurant and requires that participating players not promote other restaurants, OK. Otherwise, they should both be happy the player is at BYU and getting paid for it.