I have to say I've heard that a ton of times from Dealerships, the next words out of the reps mouth to a customer would be "but it doesn't if we install it"....BS.
As an Installer and a ex-installer of breathalizers for the government, I have been told that from dealers when dealing with leased cars for my customers and trying to get a letter of permission from the dealership to install. They have told me "We will install the breathalizer" and I laughed and said you contact the government and tell them that and try to get your hands on a unit .........lol.
So the short answer is No it does not void your warranty, if done by a licensed Installer and everything is done properly especially the bypass of the anti-theft Vats, Passlock etc.
Its just a way for dealerships to scare their customers and make more money.
For a remote starter install that would cost you a couple of hundred dollars anywere else, the dealer will usually double or triple the price and pocket 80% of the profit by contracting it out.
92 Bonneville SSEi - Stock - Remaining repairs needed due to neglect by previous owner - ABS/Trac, AC.
Mods so far: Maganflow High flow Cat, Rebuilt */C
Future Mods: Interior swap for Leath, High Output Altenator, Crazy system, Climate Control swap & Custom Exhaust/Intake.
98 Dodge Stratus - Wifes Daily Driver
92 Dodge Shadow - My Winter Beater