I'm not on Mac, unfortunately. I couldn't find anything on the web site showing how the integration happens or works. Presumably it is completely transparent.
I'm a newbie to tmux but I use it with iTerm and I love it. I use my macbook for work but my dev code/servers are on a linux desktop. When I get into work I ssh to my linux box and type "tmux -CC attach" and my tabs all re-open like normal iTerm tabs and my subdivided terminal windows all restore to right where I left them. It's great for leaving all my watches/running code/tailing logs all open and in panes. It used to take me a couple of minutes to re-setup everything when I got into work but now I just run 1 command and I'm back to where I left off.