Don't need full-time 3G nor want to pay for another account, but it would be great to tether when needed to an existing account.
Any one know if the WiFi only GTab can be tethered, like to a Droid X?
If your using WiFi, you should be able to connect to any WiFi source whether that is your phone, your router, Starbucks...
If your EVO can act as a wifi hotspot (either with Sprint's Hotspot option or with a rooted hack/program), the Tab will connect to it via wifi. What I don't think you will be able to accomplish is tethering the EVO to the Tab via a cable.
I just received my Galaxy tab a few days ago and it tethers with my EVO with no issues.