YES! And Mail.app on OS X actually works better with FastMail's Archive than it ever did with Gmail's (in my experience).

Here's a screenshot from Mail.app: https://files.app.net/1/79773/aTOWGMJ-rQ2Js_Edg-CWLi5FsLEVYq...

I either never knew that existed when I tried Mail.app with Gmail or it didn't work. In any case, it works perfectly with FastMail's "Archive" folder.