You can factory reset a rooted phone...
Yes but there is no guarantee that the reset will stay rooted. Plus given the fact that he stated he was on Samsung's ICS OS, I hightly doubt he is rooted since he doesnt realize that it is not Samsung's OS to begin with. It is Google's OS with the Samsung TouchWiz interface put over it.
So you assumed that it was rooted for what reason? Just by reading his first post I can tell you that he is not. He wasnt trying to flash anything on the phone, it just glitched into a boot loop. I have had that happen before.
To the OP:
First power down the phone. Take out the battery. Write down the information from the back of the phone. The Serial Number and Model number. BE EXACT! If it is capitalized, make sure you do that. If it is lower case, make sure you write it as lower case. Yes it extremely matters!!!
Next put the phone in Download Mode. Hold the volume down button then hit the power button.
Now start up the Samsung Kies Software. Make sure you have the latest Version installed.
Under Tools select the option to upgrade the firmware. It will ask you for the Serial and Model. This is the information you had wrote down at the start. It has to be input here exactly as it is seen on the back of the phone.
If you wrote it down right it will start the process of flashing the latest version of Android for your phone onto the device.
*Note*
Yes this will erase EVERYTHING on your phone currently.