Sorry if this is a stupid question, but I want to send my game to a publisher, so I want to test my game with AdMob and HeyZap. To do that I have to make an account on their website. But if the publisher decide to publish my game, is it the publisher who will use their own admob and heyzap accounts, or should it be my accounts who use it then?
The publisher will use their own accounts. But you should definitely open accounts for testing purposes at least.
Test but don't send testflights out with ads in it. Nobody wants to test your game looking at ads. Betatesters and publishers want to look at your game, not ads.