Are you talking about hunting with a dog, or are you talking about tracking an already-wounded deer with a dog?
I've been involved in 4 different tracks with 3 different licensed dog trackers--they are super cool and I'd go any opportunity I could. Our state requires any dog tracking to be done by a licensed dog handler--and all of them have used a handgun of some sort. 1 tracker was the daughter of another tracker who since passed away--she uses her dad's glock 10mm with a laser sight. That accounts for 3 of the tracks and 2 trackers. The other guy had a .41mag single action revolver. The dog is required to be on a leash so I have to think a long gun would just be in the way. The laser sight made perfect sense to me as it's usually in the dark, and the hunter is not allowed to bring a weapon with them tracking after dark unless specifically accompanied or ok'd by a warden. Hunters are not allowed to use a laser sight here either.