I just saw an AI enemy move their unit into a tile already occupied by another of their units.  This was not a "pass-through" where it allows one unit to pass through a tile occupied by a friendly unit to get to a tile on another side -- rather, one unit moved to a tile already occupied by another of their units, ending its tactical moves there, and a third unit moved into the same tile.

I have also noticed units of hostile factions co-occupying tiles on the strategic map ... in fact my own units have done it, after completing an attack order the game will sometimes move my unit to the tile I attacked (without a separate move instruction), even if there's another enemy army in that tile (putting both my unit and the enemy unit on the same strategic tile).