Apparently they are compatible, I just found an ad on CLs for Frenchie/Yorkie crosses - of course, I don't think that's the sort of compatable you were asking about.
Honestly, I don't see why they wouldn't be, just find a pup with a personality that works with the Yorkie you already have. And then, take lots and lots of pictures of them and post them so I can giggle along with you as they play.