Hooters can get away with this, because their entire practice is based on one thing. Luring in people (Mainly men) with well endowed waitresses.
In their case, breasts being a requirement is no more discriminatory then Generic Company #1 requiring a person to have a Generic Diploma 1 and 2.
Say I own a restaurant that serves ethnic food, and I want my patrons to feel that is authentic ethnic cuisine, so I only employ people with the same ethnic background as my food. What then?