Yes but probably not in a Canon sanctionned way. That said, the app you mentionned also costs 4 times more than FPV and their .x upgrades
are $100 each. Perhaps they can afford the risks and support costs associated with updating metadata directly within raw files at that price level
We still might look into this for a future version, though, when we reach a feature level where FPV directly competes with them. If you look at the roadmap
we'll get there, eventually... still, raw metadata editing is a risky business and some users explicitely avoid software that can touch their raw files in any way.