Hello Sukeban!
Yes, Ogata can be romanced! Like what Inkarmat says, "Well then, you can't be too forceful towards them or act like you're always sure what they're thinking. You need to be patient and observant when it comes to figuring out how they feel. If you act too boldly, you'll only make them distrustful of you."
Ogata is admittedly the hardest route, but I do think that's very in-character for him since he has had a lot of issues with love in the series. Try to think on what he craves the most and see which responses would lead him to be more comfortable with you.
Good luck and I wish you all the best in your quest for cat man!
P.S. He's the only ending where you can "sleep" with a romanceable.