@ Lunar... I've heard that before now you mention it.
@ Graimasc... The claim isn't that it makes anything "invisible", just that it reflects back and therefore masks the detail. Hairspray on somebody's hair, which is individual strands, will reflect less due to the structure of hair.. it's a fibre not flat smooth plastic. Therefore the photo would still represent the persons hair.
Saying that, like you said it would be simple enough to test. I might do so (when the snow stops!) just out of curiosity.
Will post my findings unless somebody beats me to it.