After looking around at some pics on the internet, I think its scale. I've had scale on other plants though, and they were a lighter color and flatter. On this plant they're a darker color and rounder. I'll try a spray (neem, etc.).
@bob - its grown outside. And i think just about every plumeria here in hawaii has plumeria rust, so i use a fungicide on this one about three times a year to keep it in check. you say that plumeria tend to not have pests, but scales are insects, right?
@crabber - my screenname refers to a book called The Orchid Thief. I don't actually steal orchids