I've never used ReaPitch to do this, but I'll try to explain what I think you do.
And my REAPER is an old version (Way back with 3.75 because my parents don't let me update any of my software, ugh), but it should be very similar if not the same process.
Now, between notes C4 and C5 in UTAU there are twelve Semitones, and twelve Semitones equals one octave. Therefore when pitching an off vocal, for every semitone up or down you must move the off vocal that many semitones.
So, in ReaPitch you ONLY touch the Semitone bar. Let's say you moved the song down five notes to make your male sing it better. In ReaPitch you can either subtract 5 semitones OR add 8 semitones. Decide which one sounds better, though it'd probably be the one closest to the original pitch.
Hope that explanation worked! (I didn't realize it'd be so easy myself)