This may take a while to explain so bare with me.
For a start, I would question the chances of a situation occuring where your wife/husband wasn't a virgin. Only because if you are that different in morals I wonder how many people would fall in love, to the point that marriage is a possiblilty.
However, I know it does occur, and for those people I don't think it would stop a marriage from happening, but rather would put a strain on the marriage once married. I would be constantly worried as to whether I was being compared, and whether the other person only thinks of me ect.
I think it would create a lack of trust at first in that one person was able to hold out and the other wasn't (eg if they can't wait for me until marriage, then how can I trust them after marriage?). It's something that can be worked through however, and I don't think it would stop a marriage from occuring as long as both partners are willing to deal with it and work it out together.
I think the most often time that this situation occurs is when the person who isn't a virgin decides that they don't want that lifestyle anymore and decide to wait from then until marriage before they sleep with anyone else. In this case the moral values of both the virgin and the promiscous one match up and they are able to fall in love.
I really hope that is clear, I have a feeling I will be mis-understood