Josh brings this up in episode 2.6 but I don't remember him finding out and Aiden has been really secretive about it. Also they didn't really explain how Sally's mom's boyfriend knew Aiden was a vampire. I'm sure I missed something there.
"By law you have to call it a lair if you use it to torture people." Douglas Davenport
The characters do talk off screen. Having some representation in the police is an important box to check when it comes to vampiric control of the city. So assuring Josh that box is checked would be basic how-it's-going type information. It's not that Aidan was being secretive, it's that he wanted to make it clear to "Bishop" he was not the one that personally turned the cop.
Aidan could see Sally's mother's boyfriend and was very pale. Stevie also asked Josh if he was a vampire. I guess ghosts in Boston run in to vampires more often than werewolves.
Darkness... And then laughter. Yes, tears and then laughter. Laughter always saves you two! .