that would fall in the category of risky as all hell...
Regardless if the club is 18+, you don't know if they got in without proper ID. If your intent is to put them on your site, you need a release to use their image. If you're working in the area of needing 2257 docs, then you know how much you need to have on file for every performer.
Now, that's the easy part... the more tricky part is the professional photographers I've heard talk about using settings like that say it's REALLY a good idea to get a release from the site owners to indicate that they are not going to try and take you to court for showing their property on your site. This goes for private residences, businesses, etc. What I don't know is if there would be a difference between the owner of a property and somebody possibly leasing the property. You may actually need a release from both.
Oh, and if anybody else gets in the shot... you 'should' get releases from them as well...
It's all a pain in the @$$, but it's also going to keep you out of legal trouble if somebody decides they suddenly have a problem with what was done months or years ago.