Of course, any aftermarket device could potentially void a warranty. But dealerships can't just void a warranty because they frown upon them. If I even suspected a dealership was out to get their customers I'd set a land speed record finding another dealership to work with.
I wouldn't bother removing it if I was taking the truck in for routine maintenance. If I had an issue with the truck, especially anything remotely electrical in nature, I'd remove it before taking it in. It's not something that's obvious because of where it's installed under the dash. I doubt they'd even notice it if they looked underneath the dash to plug into the OBD2 port. Even if they happen to notice it they can't just deny a claim or void a warranty. They have to prove that the device is what caused the issue because it was either installed incorrectly or it caused something on the truck to fail. But for anyone who is worried about it, it's simple to remove before taking it in if that makes you more comfortable.