It's too harsh to call someone that believes in UFOs crazy, but I consider the probability extremely unlikely:
1.) Why don't they just say hello?
2.) Given current science so far it seems likely that interstellar travel is impossible. That doesn't mean it is impossible. I'm the first to admit science is a constantly moving approximation, but right now ... ya, it doesn't seem possible.
3.) It begs the question why a race this technologically advanced would even bother. What could possibly be of interest or of value to them?
4.) A race this advanced is unlikely to visit in person. Observe from afar, or use biological drones (say some sort of engineered flying animal), or nano-bots we wouldn't even notice, or, or ... UFOs seems like such a projection of 1950s thinking onto a race that would likely LOL at the very notion (if they did such a thing).