He's kinda stuck on this one.
Most cowboy action shooting won't allow a blackhawk for two basic reasons: 1) adjustable sights, 2) gun design didn't exist in the late 1800's.
The Vaquero is one of the very few exceptions which are allowed in most Cowboy Action Shooting (design didn't exist in the late 1800's, but looks close enough - and meets the "spirit" of the classic SAA). If they didn't allow it, it would knock out over 50% of shooters in cowboy action. I think SASS does have an "adjustable sight" category - but cannot be sure.
I personally would not use a Vaquero for hunting due to one basic reason - the fixed sights. My fixed sight weapons for cowboy action is sighted in to the fairly light loads used in cowboy action. A hunting load will shoot somewhere else. Additionally, the fixed sights for me are fine for cowboy action, but not too good for accuracy beyond 25 - 50 yards. Others may do fine, but not me.
The blackhawk/super blackhawk/super blackhawk hunter is a great hunting handgun - but for the most part cannot be used in the majority of cowboy action shooting, if at all.
Tell him to get one of each!