Agree with what Pogster posted....
A lift shouldn't affect warranty of unrelated items....interior parts, door hinges, etc..... but things like suspension, u joints, etc it might since the lift is changing the factory specs for those items. If you install big wheels and tires with the lift, you can forget about warranty covering wheel bearings, for instance (been there, done that once). But if the A/C compressor goes bad you would be covered.
The thing is, you open yourself up to a lot of "could be affected by the lift" guessing when something goes wrong....for instance....you get a whine developing in the rear end.....or the tranny goes out.....could be that the added stress from your big wheels/tires did it...regardless of if the lift was done right or not and by whom.
I think that our Rams looks kick-@$$ with lifts but I wont be lifting mine because as much as I would love to, I need the warranty coverage to stay in effect as long as it can....
I have heard that some dealers will work with you and some will not....since if they cant get Chrysler to cover the cost for a warrantied repair they have to eat it. And they dont like that much.
As for that dealer tightening the lift kit they installed for your friend? Well, yeah....they installed the kit...they SHOULD make it right.