I tested it out, no problem whatsoever. I can describe what I've done: So I filmed some random 10-15 sec footage, in 1080p and one footage in 4k (with only 15s). I paired my GoPro App on the iPad Pro (12.9") with my GoPro, watched the videos in the app (the quality is a bit low though). Afterwards I've transferred the videos to the iPad (with the app via Wifi), imported them into iMovie and played around with it a bit. And everything worked flawlessly.. If you want me to test something else, just tell me what to do and I will try to test it for you guys, cheers!
Edit: here is a very short video, sorry for filming in vertical mode, I had to do it quickly.. And ignore my chaotic room
Edit 2: First cut is 1080p 60s, 2nd cut is in 4K (that's why it's choppy, since my GoPro only films in 15fps)