As far as I know, here in PA, if he has harvested his deer and has no valid tag remaining, and is now assisting on a drive he CANNOT be armed. That is, UNLESS he posses a CCW permit. Then and only then can he carry a firearm. Carrying a long gun would be a no-no. The main reason is poaching. If I filled my buck tag and was still toting around my rifle loaded, I'm sure Johnny Law would like to know what I'm doing. Try to convince a WCO that you're just using the rifle as "bear spray" and protection. I don't think that'd get you too far. It worked the same with coyote hunting. I am not sure if they changed the law yet, but to be yote hunting during rifle deer season, you need a valid deer tag to be in the woods yote hunting. Again, main reason being is our resident slob hunters who may just use the yote as an excuse to be in the woods with a rifle.
As far as a carry gun for black bears, I've honestly never worried about it here. I've thought about it but not worried about it. That's not to say I won't go armed, just usually not. When I do, the largest caliber handgun I have is a Dan Wesson .357 (one of those "dreaded" guns w/o the interchangable barrels, but I absolutely love the gun. It's the most accurate and reliable handgun I own).