They should. There should be absolutely no security difference between a Bluetooth keyboard and a Bluetooth headset (reported to be working with the 7290). Plus a keyboard driver is easier to program than a headset driver too :D
And as a deaf guy, I don't use the phone in my Blackberry anyway, so no benefit for Bluetooth headsets for me.
I received some potential good news, about Blackberry being permitted to work with other Bluetooth accessories, so I am crossing my fingers. In the meantime until this is confirmed, feel free to post in this thread
saying you're interested in Blackberry compatibility with external keyboards. :D