So, it would appear that with the updates to BlackBerry Bridge v1.0.5.6 and BlackBerry Tablet OS v1.0.7.2942, third party BlackBerry PlayBook apps now have the ability to connect to the internet via BlackBerry Bridge in the absence of a WiFi internet connection.  I tested this on multiple BlackBerry PlayBook apps including Facebook, Poynt, GeeReeder, and BlackBerry news and they all appeared to work even though the connection seems to be extremely slow.