So it appears that there are at least two music clubs in New Orleans that have free Wi-Fi. Carrollton Station is an uptown venue that is mostly frequented by college kids, and dba is a club just above the French Quarter in the Marigny section. I’ve tested the Wi-Fi at dba, but I have not yet tested Carrollton Station’s signal, mostly because I just found out about it (they now prominently mention it in the ad they run in the local alternative newspaper, Gambit).
P.S. If you want a better practice, check out this Ultimate Guide.