Is it possible to use a Google TV device without a TV connection?
Yes, you will be able to use the Logitech Revue Google TV unit without the Set-Top Box.  I am doing this with the Sony BlueRay Player w/GTV.  During the set-up process simply skip the section for setting up the TV provider and you should be all set.

Here is a youtube video of a Revue functioning without a cable or satellite STB.