As far as I am aware, SQL Doc shouldn't impact the performance of a server at all providing of course that you don't have the tool installed on the server itself.
It certainly isn't anything I have come across before, however if you are very worried about it by all means download a trial version and run it against a test DB. I really don't believe you would see any performance issues though.
With regards to updates, the only updates it would perform on the DB would be if you were to alter any of the MS_Descriptions on objects. If you altered these through the tool then yes, it would be performing an update on the database schema.
Hope that helps!
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