I fixed issue with not respecting Margin and Padding in tile set editor preview a few weeks ago in /EpicGames/UnrealEngine/commit/75967837b7621bac4542577daa9bfeb193da3733 (will be a part of 4.8). tile set view still shows padding but rectangle offset and size is now correct. I may add an option in future to toggle a ‘compact view’ that shows it as if you made a tile map out of tiles in tile set texture.
Cheers,