I might be wrong on this but i think you will find that a diector can sub work to a company that he owns and pay they on a layoff for the work done. but as to being his own subcontractor i think that will be a no as he is charging himself to do work that he is already being paid to undertake.
Your best bet would be to nip toa bokk shop or libary and find a book on employment or contract law and this will detail it. I think from memory it would amount to a conflift of contract interest, at least it would have to be contract written and disclosed to the client or would be classed sa fraud.
hope that this helps.
Proud to be Practicle not Political.