Rick will have to figure that out for his purposes.
Generally, we can't really answer that without knowing the specifics of the venue. For example, there are locations where city or town ordinances prohibit musical performances at public venues within the delineated or historic zones. Hence - a meeting or event space in that zone would have to comply or risk a loss of their license. These ordinances are NOT specifically about music - they often site zoning, traffic, building regulations, commerce and other considerations. While it may be perfectly fine to host a wedding reception, a wedding "party" may not be the type of client they want or can accommodate.
A business that is licensed as a restaurant can easily host a wedding reception for dinner but, may be legally prohibited from live music, DJs, and dancing. Could they accommodate a trio or chamber music? Perhaps even a first or patent dances? Probably, but it's impact and character would still have to fit within the confines of their license as a restaurant rather than an event space.
DJs are obviously focused on the "party" aspect of a wedding - but there is a much broader hospitality industry surrounding weddings than what is seen by your typical wedding Dj or band. It's not unusual to find softer styled brunch events or dinner receptions (sans entertainment) associated with weddings. Especially 2nd marriages, and older couples. "Boutique" style receptions often do not use bands or DJs.
If the venue truly did not make conditions like these known before closing, then a penalty free cancellation is warranted. On the other hand, if the client is merely trying to push the envelope in a space where there is no room for deviation and that was disclosed prior to booking - cancellation fees could easily be defended if worth the pursuit, (This is typically true with highly regarded and popular sites.)