Not sure what you mean by "functional" Air certainly passes through them.....and if that's your definition then, yes, they're functional. If you mean instead does the air get used in some manner downstream then I think you'll find that sometimes it does, sometimes. not.
Perhaps you're asking if the ducts are just painted on...or they're just a bit of platic glued to an otherwise continuous panel, well, most are "functional"
Hope that helps.