I'm not really sure, in "And then there was shawn" they did a horror movie spoof, and shawn was talking about how the virgins live and he was saying that he'd probably get very close to dying and then angela said "you're dead" implying that they did have sex
It's never said whether or not they do, but it's likely. Shawn is apparently still a virgin in the episode "And Then There Was Shawn", but Angela dies. Later on, they almost have casual sex in the episode "The Truth About Honesty", so that could mean that they've had sex before. Later on, in season 7, they live together for a while, so they probably did have sex.
In my opinion, I think they did, because there was one episode where Angela tells him "let's do it". or something.
and another episode in the last season "There no such
thing as a sure thing", they made out most of the time, so I
think they did.