Depends on how the word is defined. All the dictionaries I've consulted offer multiple definitions, but the gist of them is that a prophet is simply somebody with a divinely inspired message, it doesn't necessarily involve predicting future events. Buddha would qualify as a prophet under many definitions. Dictionary.com offers this, for instance:
1. a person who speaks for God or a deity, or by divine inspiration.
2. (in the Old Testament)
a. a person chosen to speak for God and to guide the people of Israel: Moses was the greatest of Old Testament prophets.
b. (often initial capital letter
) one of the Major or Minor Prophets.
c. one of a band of ecstatic visionaries claiming divine inspiration and, according to popular belief, possessing magical powers.
d. a person who practices divination.
3. one of a class of persons in the early church, next in order after the apostles, recognized as inspired to utter special revelations and predictions. 1 Cor. 12:28.
4. the Prophet, Muhammad, the founder of Islam.
5. a person regarded as, or claiming to be, an inspired teacher or leader.
6. a person who foretells or predicts what is to come: a weather prophet; prophets of doom.
7. a spokesperson of some doctrine, cause, or movement.
Buddha I think would qualify under definitions 1, 5, and 7.