Hi there! It can indeed split DLC tilesets, but unfortunately only those I've added manually to the program. This means collecting and adding each individual tile, one at a time.

Thanks to some feedback I've had recently, I'm going to add a "quick split" feature - this will attempt to split tiles in a manner appropriate for a tileset type (for A1 to A4), or just at the base tile size - 32 or 48 pixels.