There is no one correct cuck's role as there is no one way of cuckolding that fits everyone's circumstance.
Some cuckolds may simply sit home watching TV while their wives go out on dates. Others, like TwoBiFour, may enjoy an all equal playful threesome approach and then there are those, like myself, who are in D/s relationships in which the husband is submissive to his wife. There are also reversed D/s relationships in which the husband is dominant and shares his "slut" with others and a myriad of other styles of relationships.
Just as the husband and wife need to find the relationship that works best for them and their desires, so too must the stud find the appropriate couple that fits his desires and he theirs, as well. When it fits all three well, it's magic.
As a sub-hubby my "role" would be no different whether my Wife was cuckolding me or not. I serve her, her needs, desires and pleasure. I cook, clean, repair, garden, maintain vehicles and home, act as butler, secretary, lover, pain slut and anything else that she requires of me. Should she take a lover and choose to gift my services to him in whatever manner, than that becomes my "role" as well.
However, my "role" is what works for us and doesn't necessarily apply to anyone else as it is no more right than any other.