If you make it's collision size = 1 i think you can make it go "almost" through other units. And if your doodads and destructables are near enough, they shouldn't be able to walk through. Unit won't go through cliffs if it's not a flying unit.
If your request is an ability, then try basing it on Wind Walk with -1.00 Transition Time, so the unit won't go invisible.
I still want the unit to go transparent without being invisible
50% transparency is the same as invisible units, I think.
- Animation - Change Unit's vertex coloring to (100.00%, 100.00%, 100.00%) with 50.00% transparency