There have been comments about this in other threads, I think. The general consensus is that you probably can't "void" the warranty, but what it WILL do is give your dealer a crack in the armor to try to talk their way out of doing a repair, if the problem involves something you modded. The remote starters IIRC don't actually connect to your starter, just your electrical system, but if you then suffer an electrical system problem--even if it's nowhere NEAR the remote starter--they can say, "Well, lookee here, you added a starter and modified your electrical system, so we're no longer responsible."
Technologically, it shouldn't be a problem. I have a manual transmission that I had a starter put on in 2003. I have to go through a convoluted process to make it work, LOL, but it works. (I have to press one button while the car is still running, then turn off the ignition and remove the key but the car is still running, then get out and shut the doors, then press a second button to turn off the car. And I can't re-open a door or it ruins the whole process. Then I have to press one button to remote-start, then press a second button to de-arm the doors so I can get in.)