Yes, NFL ST online is supposed to adhere to normal Sunday Ticket blackout rules. The games that are available on your locals should not be available to be streamed on NFL ST.
However, a few years ago I found a strange loophole. Not sure if this still works, or if it even worked for anyone else beside me. A few years ago when Verizon was my wireless provider, I had a Moto Droid HD Maxx phone and a Moto Droid Xyboard tablet. Using the NFL Sunday Ticket app on the phone resulted in always being blacked out of local games, no matter the circumstance. With the Xyboard tablet, I'd be blacked out if I used the tablets built in cellular radio, but if I tethered it via wifi tethering from my phone I had no problem accessing games that I was not supposed to be accessing. If I was at home, connected to my normal wifi, as expected I was blacked out as well. Not sure how or why this worked, but I used it the 2 or 3 times I was dragged away from the TV to stream Bills games in the car.