After obtaining eyelashes from the Arks last Stand scratch, as well as purchasing new eyelashes from other players, I can confirm that neither seem to register to the Salon if you have a maximum of 90 slots registered for eye-lash cosmetics in the salon. It's possible other cosmetics may have a UI limit as well, so before you consider buying cosmetics, please check your salon to see if there are slots available. The result of using coupons if the limit has been reached is that the items cannot be selected in the interface of the salon. There is no UI to cycle through other pages in some cosmetic categories either, and the cosmetic coupon is used regardless.
Edit again: Never mind, discovered they're actually eyelash "accessories", not actual eyelashes.