Yes. There are no additional constraints for App Designer, just the same constraints as otherwise.
Remember though that "app" is an object. The way that objects are transfered to workers is by the equivalent of save() on the client and load() on the worker. If I recall correctly, "app" has some fields that cannot be saved -- which if I understand correctly means that you effectively cannot use app inside your parfor loop. If you need fields from app save them into local variables and access those variables in the loop.
App Designer has the same restriction that other kinds of graphics do, namely that graphics in the workers cannot affect graphics in the main function. It isn't that you cannot create graphics in the workers: you can, and you can save the graphics as images or export_graphics() or similar, but they will not affect the display on the client.
