Unit selection and collision Box

I need to make a unit non-slectable. So, after some thinking I decided to go to the code and put some changes to ignore the unit on the selection functions, based on a flag. Speaking a little more technically, if the flag is false, I just dont pass mHitInfo, so the given unit never reaches mHitObject. But with the changes almost finished on guiRTSTSCtrl.cc, I got this doubt:

Isnt enough for a non-selectable unit, to just dont give to the DTS a collision box?

I dont get much about collision yet, so if ayone has a clearer idea of this point would be of great help.