Hi D Fosse (and everybody else) are you still there? You won't believe, but I am having the oposite problem! I have some tiff, and they have never been converted to PSD, and I can't open them in raw. Actually, they are scans from the lab. However, they have been in raw sometimes in the past, yes, and they are still tiff. Using your precious info I went to:
Photoshop pref>file handling>prefer camera raw for jpeg and supported file, (I know, they are tiff, but just in case): CHECKED
Bridge pref>thumbnails>pref adobe camera raw for tiff files: CHECKED
Camera raw pref>always open jpeg tiff using camera raw: CHECKED
But the magic didn't work.
What version of Photoshop, Camera Raw & Bridge?
From your description I suspect it's CS3 (since in CS4 the prefs are all now in Camera Raw)...
If so, try purging the cache in Bridge and make sure the tiffs have no layers and are RGB files.