Happy New Year, Libby!  I have also struggled with these types of requests from community groups.  We had a couple musical groups come into the main lobby to perform during the holidays, and I had them all sign a non-disclosure form.  I tracked their service as a group in Volgistics.  If we had a group coming to serve strictly outside the building, I would not require any forms, just a list of all participants.  If I anticipated they might need to come in to the facility, I would give an explanation of the reason behind the non-disclosure and have them each sign it upon arrival.

Great question!  I'll be curious to see what other hospitals do for groups.