Yeah, I'm thinking either individual defectors or small groups of half a dozen or so are probably more likely than entire units deserting en masse.
On a semi related note, James Langham put together a really good piece a little while ago on Dutch auxilliaries in French service. If you haven't already come across it I'd recommend reading it if you're interested in this topic.
http://forum.juhlin.com/showthread.php?t=2648