OK, this is one of the few times I haven't read a whole thread before replying to a thread so I apologize in advance for that, but I just couldn't go through it all.
Forget you know anything detail wise. It doesn't matter what your opinion or morals are... this is job related and needs to be separated, anything else will cost you your job which I doubt you can afford to lose. You need to filter names out of the equation.
If you want to avoid the dinner, make an excuse, and don't socialize with them as a couple in the future. Yes, youll probably have to explain at least some of it to your wife and I dont condone keeping secrets from your spouse, but Ive worked in a job where I couldnt share details either. Theres a fine line and you need to walk it, you need to find your best path in YOUR marriage, but your friends marriage is NOT YOURS!!!
Yes, you can engineer it so the husband will ask the right questions and you can act as if you are 'forced' to say something, but that's just a petty act on your part and no better than taking an add out in the paper with peoples problems. You'll be living up to all the expectations about small town dispatchers/cops who can't keep their work separate from their day to day life.
I agree that marriage is a sacred bond, but it's not YOUR marriage.
Live your marriage in your way, and leave the rest to their own lives or you're just a busy body snooper.
If you must confront the woman, do so if that is what your conscience demands, but you need to do it face to face and up front. Of course, you are not the only one who knows about this, and shes got to know that her behaviour is going to come out. Also, I doubt if her husband is totally ignorant of there being a problem, if you avoid them, shell know why. I guarantee theres no easy answer. If you tell the husband youll lose his friendship too, if you dont tell him, and he finds out you knew, it may cost some status as well, but will know that you cant go running around telling all about who gets questioned by the cops, for anything no matter how hard it is NOT to.