Rashi in Bamidbar 22:5 addresses Bilam's being a prophet:
"Why did the Holy One rest his Divine Presence upon a wicked gentile? So that the nations of the world should not have an excuse [as to why they didn't serve God]. They would have said, 'If we had prophets, we too would have repented.' So God established prophets for them."
To me this wouldn't seem 'fair'. If the gentiles would want a prophet to help them 'repent' why not establish for them a righteous gentile prophet?