There are varying reports on receiving OTA updates (not Froyo) after rooting.
The last update came to my phone and successfully installed a few days after I rooted and ran the stock apps "unroot" method. I later found out that my device was still rooted, simply by re-installing Superuser and checking files in Root Manager.
It appears that updates can install if certain apps and files remain in a rooted Fascinate, thus my success after running the stock apps method.
Others say the update would never install, either timing out or eliciting an error message.