These links contain the supported RAW camera lists for Affinity Photo for iPad. On the iPad build you will be using system level Apple (core image raw) engine, and Serif's Raw Engine is not in the build, so please refer instead to these articles to see if your camera is supported:
on iOS 12 and macOS Mojave
on iOS 11 and macOS High Sierra
on iOS 10 and macOS Sierra
The list of supported cameras and the algorithms used depend on Apple's implementation. New cameras will be added by Apple in iOS updates.