I don't think that Beltran hates Star Trek or hated being on Voyager. he was dissapointed over how his character were shoved in the background in the later seasons.
He had ideas and suggestions which were totally ignored by those in charge and I can understand that he felt frustrated when everything became more and more focused on Seven, The Doctor and Janeway while the other characters were shoved in the background. Note that Beltran's character was supposed to be the second most important character in the show after the captain, just like Riker was to Picard.
No doubt that he was annoyed.