A man should do what comes naturally. If the cuckold and/or his wife object, then they will object. My experience is that they are unlikely to say anything if the fucking is stellar. Big cocks and great fucking usually trump everything else. Why else would a woman fuck another man?!
One of the most bold and enlightening moves I have ever seen, and I have actually discussed this with men, is when a black man is hitting on a white woman who is out with her husband. If the black man will find - not a discrete way - but, a SEMI-discrete way to touch her pussy, then that will tell him volumes.
If she responds even neutrally, then odds are she is on board. If the husband responds positively, or more likely, looks away, then it is game on. The worst that will happen in almost all instances, is there will be a scene. Most white men will not escalate something like this very far and will deescalate it very quickly.
So, be bold. Touch her pussy. She's already talking to you. You are already hitting on her. Pro or con, she won't really be surprised that much.