There are many factors involved here. Foxtrot & Hoser can likely identify the requirements better, but, to my understanding, once the site officially endorses a shooting event we accept certain liabilities and responsibilities.
Off the top of my head, I believe the following applies:
* We'd have to ensure site staff are on site at all times.
* We'd need participants to sign Hold Harmless / non-liability / participate-at-own-risk letters.
*We'd need to ensure we had competent (preferably certified/trained) RSO's actively involved.
I'm sure there's more, but it's outside of my area of expertise.
As fellow shooters, we're always happy to see our members get together to enjoy our common hobby but "sanctioning" the events is a whole nother matter.