Pretty much all the match ammo I’ve seen is “standard velocity”. I haven’t done a lot of rimfire and no comps but all the “premium” ammo I’ve shot (eley, Sk, wolf, lapua, rws) are all standard velocity.
dug around the site and found a page with more info and details:
https://www.rbgc.org/content.aspx?page_id=22&club_id=265856&module_id=471047
NRA rules for rifles (looks like max 10 pound weight including optics, 30" barrel).
given what I've seen so far with River Bend if you show up with anything close to what you need and a good attitude you'll get setup with anything extra you might need to have a good time.
and yes, all matches are open to the public.
In for info. Will be a few months till I get my rifle but want to shoot a match or two this year after I get some practice and dope on the new caliber.