Yes, even the “frum” halls, will allow a few mixed tables. We had that at our wedding. Regarding the men seeing the ladies dance, there is usually a “natural” Mechitza of ladies standing around the outer circle anyway so that it is very hard to see anything anyway. And yes, as mentioned before, if men want to look in, they will look in, even if they are in separate halls.
You also have those “frum” couples, who will only bring their spouses IF it is davka mixed seating, since they will enjoy a night out together (yes, a novel idea in the frum world!).
All in all, this topic can be discussed for days/weeks – it started out as a nice Chumra and now evolved into something larger than the Simcha itself unfortunately.
Mazal Tov!