Yes you can.
I am currently using a Motorola back flip which is near useless and tethering the internet (Grandfathered Unlimited) to my Motorola Xoom.
For anyone else wanting to do the same I would highly recommend downloading PDANet Tablet off of the market before AT&T decides to try and censor it. So far there have been a few slight stability issues but that's what you get for running a beta app. The trick is to make sure to connect the server/client first then go back into the proxy settings and press save. For some reason this refreshes the proxy settings after the Bluetooth connection is made. This post was made via my xoom wifi only compliments of AT&T's wireless cellular network.