IIRC, it is an appointment process that by definition does not require the typical competitive hiring /posting processes.
Best analogy is when the Governor selects Commissioners. There's no posting requirements and the process is outside the requirements of Civil Service. I believe that extends to the coach's staff just as Commissioners are able to name Assistant Commissioners without going through the Civil Service requirements.
There's no pre-established salary range either! BTW, had it been within Civil Service requirements, Saul's hiring wouldn't have been permitted under anti-nepotism provisions.