Didnt FoT itself have such feature?
Because - as Graf wrote above - the FOnline engine supports tiles, critters, etc. from Tactics.
It support tiles etc, but does it support the different heights/levels?
Take a closer look at the video again. The player is moving to the place, which is over the ground level. So I assume, that the engine itself (by default) can't do it, but this feature could be implemented.
These are "just" fake multilevel maps, done via some graphical tricks and illusions, not a real native tactics multilayer map.
In knocked-out state, the player shouldn't have any weapon in the hand anyway. :p
Why not? In my opinion it looks very nice. It just needs some little tweaks.