They were married from about 1970 to 1990 ( or there about ) so it is concevable they had sexual intercourse.
Did Masters and Johnson have sex?
Considering they are famous for the research they did into sexual intercourse (especially what it is like for a woman) and like John said they had a relationship and eventually got married, the likelihood of them having sex is PRETTY HIGH.
By the way, there's a TV series about them that I really like (even though I only caught the first couple of episodes and really need to catch up)!!
Here's a trailer though (WARNING: Slightly raunchy)