I leased 3 pickups, one of which I added a class III hitch to, and one of which I added a 5th wheel hitch to. I had no issues as at when returning either Ford pickup. A lot of leases have a damage waiver included (like bring it back with up to $2,000 in damage) but I don't think that even came into play. They expect you to use these vehicles. Bring it back with the door caved in, going to cost you, bring it back with a scratch on the top of bumper because the DW dragged something out of the trunk, normal wear and tear. I'd just ask the dealer outright. Also, when you say leased tow car, do you mean a toad, or a tow vehicle? If you mean a toad, the only issue I could see is possibly putting on miles if you have to have the key in the ignition and you're flat towing.
Loving our Sierra 365SAQ
Nights camped so far in 2016 = 0
Although Many trips scheduled.