What about muddy areas on maps that slows the movement of vehicles and bots, but allows hover to pass unhindered.
#mud/marsh
inland fog
stray escarp
I believe shallow water has this mechanic?
misty horizon
I mean that can easily be done, with one small problem tho... Raptors are hovers xD
livid aurora
animals/reptiles tend to traverse muddy/swampy terrain very well
tired horizon
This is already true on some maps I believe, but the effect is more like 90 % movement speed rather than more visible hindrance.
inland fog
If you wanted to take it one step further - what about areas that start as grass, but can be churned into mud if too many units pass over or if hit by to many shells? I think mud could give hover a but more viability and make for more dynamic play. Obviously you would not want mud on every map, but if there is already a mud mechanic maybe more of a movement penalty is needed. Or even the possibility of units getting stuck.