It is highly unlikely that sperm could introduce an infection, whether your cervix is dialated or not (but if you do have concerns ask your OB to make sure, but my MW never mentioned anything like that as an issue.)
Lol, and with my dd, my labor was induced through sex. It caused the water to break, an hour and 3 pushes later I was holding my baby girl (I was full-term 37.3 weeks). NOT that I am recommending this for everybody, but I must say, personally, it was an enjoyable (and unforgettable
way of inducing labor.