"Developed stored procedures for an international banking organization. During this project I used PL/SQL and was exposed to domain knowledge in low latency transaction processing. Familiar with ACH protocols and international wire transfers."
"Designed, developed and maintained a relational database servicing 3,000 client machines processing 46,000 transactions per day with high throughput and low latency for an entertainment company based out of Nevada."
If I saw those on your resume, I wouldn't even make the connection to gambling or illegal activity, and even if I did suspect it, who cares?
"This is going on your PERMANENT RECORD!"
Just emphasize your technology role and put some positive spin on the industry/sector, if its actually illegal then cite confidentiality agreements that prevent you from disclosing the actual company and flip the conversation back on the role and skill set.
Real Users find the one combination of bizarre input values that shuts down the system for days.