I wired my Tone rear door popper to a stock Isuzu tailgate release switch like you are proposing, but the one thing that I found was that if you connect the pin switch to the dome light AND the little open indicator light on the stock switch the popper will not work if the dome light is one. In other words, if you have one of your doors open, which turns the dome light on, then the stock switch will not activate the popper. I don't know if it's just the way I wired things, or if there is some kind of mechanism in the stock button that canels it out if the indicator light is on.
The only way I can see around this would be to install two pin switches; one to turn the dome light on and one to turn the open indicator light on on the stock button on.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless