Not sure about the harmonizer. I have discussed his vocals in the past just to make sure I was giving accurate information, because some have mistakenly accused him of lip synching rather than singing. I can understand why people might thing that, because they use a backing track that is either mostly or entirely James, and for MOST of the parts where JP sings as well, he likes to be VERY low in the mix. Here is what I said in another thread:
If you happen to be close enough to him during the show, you can hear him singing. But they do use backing tracks for the vocals, and JP's live vocals are low in the mix. That is the reason you are primarily hearing "another James" and the backing track. JP sings his parts to blend in, not to stand out as another singer.
Interestingly, the backup vocals themselves are fairly low in the mix compared to the other instruments. You might not notice during the show, but during sound check, James often doesn't sing, so you can really hear the backing track, and it's surprising how low it is in the mix. But you still hear it, and your mind kind of fills in the gaps.
EDIT: Oh, by the way, I was at the same show.