I spoke with my advisor, he said just keep your receipts along with a log of miles and date and you will be fine.
To deny a warranty would have be oil related, such as you didn't tighten the oil filter correctly and it leaks and you drive without oil and grenade your motor. Or they find your oil is super dirty because you never changed it and it caused a problem with the valvetrain in the motor. Those kinds of things. I've never had an oil change at the dealer and they have never questioned a warranty issue I had because of it.
I honestly don't trust them to do my oil change correctly. Oil techs aren't paid well and they don't care about your car. Things I worry about... not draining the oil all the way, not using the oil I paid for, not changing the filter, stripping the drain bolt, turning on the engine without any oil because they forgot to put it in (happens more often than you think), checking my air filter & forgetting to put it back in, overfilling the crankcase, dinging my door on the lift posts, getting grease stains on my seat and all kinds of other stuff I can't think of right now.
When you change your own oil, you know it's getting done right, the way you want, you know that synthetic you paid for is being used, that you replaced the filter and that the oil level is right.