dealers will say 1 of 2 things. 1) they will warranty a lift that THEY install. Mind you, it'll cost you about 1500 just for labor and about 2x the normal price for a lift that will suck anyways((probably a Rancho lift)) )... 2) They might say that they will only warranty a lift that they sell and installed by one of their 3rd party installers( Dick Cepek is one)... Then after you have a 14.00 hr mechanic who can care less about your rig because he has child support to pay installs your lift (incorrectly) and you have an issue, don't be surprised if that warranty you protected.........is void.
Ask me how I know
If you want a lift, do it right, have a garage wrenching party and say screw the warranty. My tj is 17 yrs old and to this day I wouldnt need anything covered by a warranty. You don't think that 35's, and ANY sign of offroading would void that warranty anyways?