Actualy you are the first one I seen ask flor this option, I do not think any of the video char apps support this ... I guess this option could be useful somewhat.
i guess i've never even considered this either. i gigure if i'm close enough to the device to be video calling, then the speaker works just fine. it would be a nice option though.
Here's a version of Tango that supports Bluetooth:
http://tangohacks.com/viewtopic.php?f=3&t=3