As a site owner who does risk assesments I can see the use of rec balls as an issue. I can see the benifits in a sports hall for pratice for sharp shooting etc.I can imagine there being a big issue if you started firing them at each other thought. I for one would not allow anyone on site to use rec balls if they were shooting at each other. This goes even if the guns were running at 180 fps if they were using as a way of saving money on sharp shooting and speeding up trigger fingers etc then no problem at all.
Why wouldn't you let people use them to shoot each other? We train versus each other and havn't had any problems.