Various Splatter Generators/Textures
Can I use the generators directly in Blender?
No, you can open them with the free Substance Player and customize your own textures up to 8K which you can use then inside Blender.
Is it just a mask/alpha texture?
There are 2 textures to export, one simple B/W Mask and one B/W heightmap.
Is it possible to make just spritesheets or also single splatters?
You can do both, just single splatters or spritesheets with multiple splatters on it.