As an Ole Seagull sees it the answer is “No”. The Merriam-Webster Online Dictionary defines the noun “Holiday” as either a “holy day” or “a day on which one is exempt from work; specifically : a day marked by a general suspension of work in commemoration of an event.”
The American Heritage® Dictionary of the English Language, Fourth Edition defines “Kwanzaa” as “An African-American cultural festival, celebrated from December 26 to January 1.” In spite of what many people think Kwanzaa is not an ancient African celebration or tradition, it “is simply a time of reaffirming African-American people, their ancestors and culture.” that was founded in 1966 by Dr. Maulana Karenga.
If one really wanted to convey good wishes to those celebrating Kwanza why not give them and what they are celebrating the honor and respect of calling it what it is and say “Happy Kwanza?” One could apply the same logic to wishing a Christian a “Merry Christmas” or those of the Jewish faith “Happy Hanukah.”