Unless units fight in melee combat there is always a spacing of N meters between them. Virtually, there is no way for two friendly units to collide with each other, while enemy units can engage or disengage to/from combat only by performing special movement maneuvers called Charge and Retreat correspondingly. There is a bug in DO when enemy units may still collide with each other during wheeling.
However, sometimes there may be situations when rival units collide with each other during wheel maneuver