update revision: 131162 added holster ability for vests with accompanying model.
when tested with diver, the holster comes with the diver uniform item so if one adds a vest with its own holster, there essentially will be two overlapping holsters.
related to thread: http://feedback.arma3.com/view.php?id=369

secondary problem: side arm does not show attached (in the holster) with the uniform only, one must wear a vest with holster model to enable side arm model.