When I lived in Schaumburg, IL for two years on a work assignment, I recall seeing a lot of these standalone banquet halls throughout the Chicago suburbs. By "standalone" I mean unattached to a restaurant or hotel. I've never seen many of these outside of the Chicago area. Some of them were quite large - they could host 3-4 wedding receptions at the same time, or a large corporate outing for 1,000 people. That was my main experience with them: we did a few offsite meetings at them during the day.

So, my guess is that this rate is related to one of those banquet halls. Since the halls don't have hotels attached to them, they likely have a rolodex full of contacts at nearby properties, along with negotiated rates for their referrals.

I know they green-lighted your use of the rate, but my only lingering concern would be if it's drastically lower than what a normal weekend rate would be (which should already be fairly cheap unless you're talking about the RI downtown), they might want to know which wedding you are attending. If we're talking about a $99 wedding rate and a $119 "normal" rate or something like that, then they probably won't ask any questions...

But based on your prior post, it sounds like you're saving some significant cash. Risk is probably still small, but I wouldn't say it is zero.