Honestly it depends how the camera is wired. If the camera is wired eg:
Horrible scenario: Butcher main wire harness to tap 12V and frayed other wires.. of course anything electrically that is connected to the main wire harness eg ECU etc won't be covered under warranty.
Normal scenario: You use a Fuse tap on a spare fuse slot and run a separate wire from the fusebox up. At most even if the fuse tap melted destroyed the fuse slot, the other slots are just fine.. then the warranty other than that spare fuse slot should be fine. Fuse taps if you don't know, are these:
Medium ATM Fuse TAP ADD ON Dual Circuit Adapter Auto CAR Auto Terminals 20A Fuse | eBay
I think it depends on more HOW you instal the camera.. more than a blanket statement just on dash cams.