Just my opinion here- I don't believe a tip is always called for on these kind of trips. There is a pre-determined amount of work that you are being charged for. The outfitter sets these prices accordingly to cover the costs of this service. If you feel an employee of the outfitter goes above and beyond what is required, then maybe a tip would be in order. For example if the wrangler gives you some of his personal scouting information that leads you to some good hunting, you may want to tip him at the end of the hunt.