Does the greeting "Good Yom Tov" contain a redundancy? Doesn't "Yom Tov" mean "Good day"? So you are saying "Good good day?"
This is a matter of idiom. "Yom Tov" while literally meaning "Good Day" is the idiom for a day that is "good" because of the spiritual level of that day. Thus, when spoken as a single phrase, the translation is similar to the English original "Holy Day" which we now use as "holiday". The Yiddish "Yumtuf" or "Yuntif" shows that it is used a a single meaning. Thus "Good Yuntif" would not be considered a redundancy. It is the equivalent of "Happy Holiday".
This answer was approved by the Department of Redundancy department (:-)