Thanks, all. It's the not-girl, not-Spanish usage I was thinking about. I wondered whether people think it's less nick-namey looking spelled like that, but don't want to use James for whatever reason? But it still doesn't really make sense to me.
Jaime is my experience in the US will be female. Until Jamie Olivier they didn't seem to associate it as a boys names and I have never met an American male Jamie. James is also not generally v. popular as a boy's name compared to the UK. Michael in comparison is massive over there and you are drowning in Michaels since the 1950s onward.