I would say that you are right on, as far as meeting in a hotel room. There is nothing else to do there. If all they wanted to do was talk, they could meet in a park or something.
Let's look at this. If you do nothing, they will meet and you will find out what happened via your snooping. If they do have sex, what will you do?
Does your W know that the OM lives with a woman? Be prepared that if you alert the other woman, you will need to go with the facts as she will not want to believe it either. Also, your W might not take this act very kindly either. I wouldn't let that stop you though.
