Spriter is an animation package for sprites, so trying to edit levels with it is probably not fair. I quite like a lot about its user interface and general performance, so I imported a Pingus level into it:
There is no way to add custom attributes (at least in the version I tried), and no way to specify groups or layers. It seems to stall whenever it needs to go through sprite data, for example after zooming or scrolling, or after changing the selection. This is most likely caused by the number of sprites, and with a more appropriate scene size for animation it shouldn’t be a problem.
I do quite like the user interface, and I imagine a more organic looking level with many animated elements would look very good. For now it may be a better idea to just animate parts of a level in Spriter and use a different editor to build the complete level.