Well, I do think that as much of a gossip as Chimney is, he still knows that some things really aren't his place to tell.
So, I think maybe he would've told Tommy about Buck's abduction, or at least the car accident, after everything was settled and he was safely back home, but not about what came after. He knew Tommy would rightfully be concerned.
And Tommy does occasionally ask how Evan is doing, but he doesn't really want to put Chimney in the middle. It wouldn't be fair.
And Buck knows they still talk, of course, but doesn't know they meet up once or twice a month for drinks. Sometimes they just shoot the shit, and sometimes they share career advice, Captain to Captain.
And he definitely hasn't told Tommy about Theo.