Hi tiggs
I think you have little to worry about as a job with Eden Futures should be ideal for him.
With ESA there was Permitted Work and Supported Permitted Work. These have now gone with Migration to UC and instead with UC there is a Work Allowance for those like your son with a disability.
Have you tried using a Benefits Calculator such as Entitledto.co.uk to predict how much better off he should be doing some work ?
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
