I've always been able to use video chat in Google Chat up until I installed Snow Leopard over the weekend. I am also able to use Google video chat in the Firefox browser since the install. I'm wondering whether others are having an issue due to Safari since the Snow Leopard install. I was running Safari 4 before and don't know if there is an update as part of Snow Leopard?
The Google Chat plugin for Safari is 32-bit. The new version of Safari that came with Snow Leopard is a 64-bit application, and launches natively as such, thus it is not compatible with the 32-bit plugin. This has affected several other Safari "add-ons" that aren't 64 bit.
One workaround is to use Firefox, until google updates the plugin. Another option is to Cmd click on Safari in the applications folder, select "Get Info", and check the box for "Launch in 32-bit". This should allow you to use Google Video Chat in Safari 4, but you lose the 64-bit advantage of stability and speed increases that 64-bit Safari 4 provides.
Firefox is still a 32-bit application, thus it remains unaffected.