Scooter/Motorcycle parking on sidewalks?

NO. Motorcycles have to park on the street and pay parking metres if needed.

Yes, but not within designated bicycle parking areas of course and they can't create dangerous situations.

Sure you can (on the sidewalk, not on the parking for bicycles).
The law has changed in 2011.
http://www.legalworld.be/legalworld/content.aspx?id=53166&LangType=2067