In the past, I have tried to mobile order at Primo Piatto (the Riviera QS) from the Skyliner and the app gave a notice that only guests staying at the resort could use mobile order. However, my husband tried on his phone and didn't get the message, and we were able to order.
We've traveled there via Skyliner for the purpose of eating at PP several times, and this has only happened once, and that was during a busier time. No one will keep you from taking the Skyliner to the resort, the only possible issue I know about is that you might get that message if you want to mobile order. If you do, I advise refreshing and trying again, or just walking up to order once you get there. If it's not the morning breakfast rush, my hunch is that you won't be turned away (to be fair, I really don't know if that's true for sure).