It should let you do the OTA without unrooting, if you have a completely stock rom. You will need to reroot after the update as it will unroot your phone.
I got my SGS3 on July 3rd and rooted the next day. Several OTA updates came out in the following weeks and i couldn't install them. OTA updates I believe require the stock recovery to apply the updates, if you've rooted then they will break when installing.
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