Ramps leading to water on most maps are typically kbot pathable, but not veh, in the underwater part which allows hovers (who don't care about the underwater part) but would not allow amph-veh. Oceanfloor on the other hand is almost universally flat which makes any distinctions void (and rightly so, because it's difficult to see the shape of terrain underwater).
The idea is pretty interesting but maps need to happen first.