First, I think the role of any CCW that is not part of the security team needs to be defined: it should be to defend your immediate family and friends and remove them from danger. If you have the "Golden Shot" to hit the BG and end the problem by all means take it, but that should not be your primary goal. Stay out of the way of the people whose job it is to stop the BG.
Second, there is nothing wrong with an identifier for security forces, but in the venue of a church, why not a bright yellow or orange armband that reads "HOST" or "STAFF" instead of full uniforms or vests? There is no reason to get the civilians stressed up with uniformed guards for a single event as long as security can identify each other quickly and efficiently. This is a nice middle ground that looks professional but remains low key.
Finally, a sniper position might hold all sorts of liability problems, but there should be major benefits from a "Security Overwatch" position that organizes communications and can keep watch over the top of the entire event. One person dedicated to watch and equipped with binoculars while another runs communications could make things run very smoothly.