Yes, that would help, its usually the first thing I tell clients to clear up any potential future "gotchas" for them.
That said, if you dont, and just do it, its almost better because then if they ever do figure it out some day (probably would by you not saying ... "I'll pray for you" incessantly like they do, or talking about what god has blessed you with etc.), it gives you even more cred.
If they are paying an annual fee to use your program, then you are benefitting from giving it in the long run. If you demand they pay, they may instead use another program. It's not about religion when it comes to finances. You're not going to prove a point by denying it to them.