I just went through my entire warranty book and no mention of drilling a hole in the door to insert an oil spraying wand will void the warranty. My dealership says not a problem since most if not all rustproofing requires drilling of holes. Only thing I can think of is the rust warranty which talks about paint/finishes being removed and not attended to but hell its a hole with rustproofing in it.
The APA quotes - Sometimes dealers erroneously claim that drilling holes will void the manufacturer’s warranty. This is misleading, and drilling holes may be necessary in order to ensure that the the product reaches the seams, cracks, crevices, etc. where rust really begins.
Just about every rust proofing business indicates warranties are not voided by the car manufacturer. Only catch I can come up with is Nissan does not want any additional rust proofing done to the Leaf.
PS - If your rust proofing business didn't drill holes, ask why and how the hell they got inside the sills, doors, etc to even apply the product. Then ask them to demonstrate.