He doesn't oversee it. No more than he oversees any of the Circuit Courts. His only role is to hand pick current judges to serve part time in FISC.
There is even a FISA Court of appeals, also not under supervision of CJ Roberts. FISC is a self-contained specialty court. Congress likes to make self-contained specialty courts.
Some would suggest you misspelled corrupt.
To suggest Chief Justice Dread Pirate Roberts has no connection, direct or indirect, to FISC is, well....absurd.
btw, Chief Justice Dread Pirate Roberts is the one who appoints judges to the FISA court – every last one of them including judges like Rudolph Contreras, who granted a previously denied Michael Flynn FISA warrant.