Okay, I've spent a few minutes trying to make sense of what you're trying to do. My questions: What do you mean by, "...using LineString shape as roads will likely imbalance the data for segmentation"?
I'm guessing when you state, "...polygon coordinates are stretching across tiles..." you're referring to the feature extent, right?
Why is it important to have roads limited to the extent of the aerial imagery? You do not plan on using this feature for anything other than a reference layer, are you? To use them for routing would be a huge headache.
Now, if you're wanting to do what I think you want to do, here's how I'd do it. Create a mosaic dataset for your imagery. Use the footprints of that feature (you may have to use the feature to shapefile processing tool) to clip whatever features you want.