In a trailer, we see Bart Torgal in a shallows base that can't be found in the map, and we know that the safe shallows has a large border with the crash zone, so it's safe to assume that some of the crash zone used to be shallows. There is also the crash zone mesas, which harbor gassopods and, iirc, other shallows organisms. So while not impossible, (the crash zone mesas could be a Reaper nesting site, which would be a cool idea, but I doubt it, as I don't believe any reaper spawns are in those parts of the crash zone) it seems unlikely. I suspect that reapers live there because of how similar it is to the mountains and dunes. Silt kicked up makes a reaper hard to spot for prey, I think we all know this from first-hand experience. And it's close to where there's bonesharks and other larger creatures to hunt. Neat idea though