In case anyone else is having this problem, it seems that the DPS tech handles scroll events the way that iOS used to, not allowing the DOM to be manipulated until the end of the event (when you take your finger off the screen). iOS has handled scroll events in the proper way since iOS 8, but it seems like the DPS tech is still a bit behind. My solution uses iScroll (specifically their Probe script) to keep track of scrolling as it happens and trigger events on scroll, namely my simple parallax script.
Here's the link to the iScroll library: iScroll 5, smooth scrolling for the web