Yep, you can add the cards if you switch root off in SU but you wont actually be able to complete a transaction at a terminal whether its switched off or not. Course a lot of people like me don't like using the phone to pay. I don't find it any more convenient than simply swiping my card and in some ways its less convenient since phones have become more bulky than wallets nowadays making them the less attractive option to carry into a store for me.
IMO if you have done it and like it you already have an answer about where you stand on it. If you haven't give it a go and you'll know whether it is an option you'd be willing to forgo root over. For me there isn't even a question since I don't like using the phone but if I did like it I still woudn't give up root for it. Simply doing nothing more than removing ads would be enough for me to keep root. To say nothing of the fact that I like to go to 4 nav buttons and all kinds of other things that all require root. Android pay would have to bring me a cold beer after work and then pop a supermodel out of my phone to give me a back rub before I'd consider it a viable alternative to swiping my card and having the benefits of root.