In my experience the "bull" doesn't want to admit he's bi or willing to say he doesn't mind being sucked off by a guy. It's happened a few times where the guy I'm with has fluffed the "bull" and it's met with moans of pleasure from him.
Once we were all warmed up then handjobs from the guy to the "bull" and also, bjs, applying lube to his cock and also eating his cum too.
Even after all that the "bull" would never admit that he enjoyed it but rather it was him 'being in charge'. I don't know if it's a guy thing or a cultural thing but I feel guys would enjoy it a whole lot more if they admitted they were bi or thoroughly enjoyed a guy pleasuring them.