Honestly, if you go far away and rotate as an MS4 and you want to apply to that program, I would make it almost mandatory to at least say hi to the PD. Otherwise when they see your application and notice that you rotated there, they'd say "well that'd odd, I don't remember student xyz, maybe he didn't like it here."
When I was an MS4 I did an away rotation at a place 2000 miles from my school. While I was there, I emailed the PD, said I was doing my rotation there and wanted to chat for a few minutes if possible. Afterward, I mentioned that I was planning to apply to the program there, and that if they wanted to interview me it would be a little easier on the wallet for me to do it while I was there. They interviewed me in October, way before their normal schedule, and I saved a lot of money.