Once its cleaned out, would a fitting like this, keep larger sticks and leaves out ? You could blow the area clean every month or so, might keep larger stuff out of the pipe. Is your pipe 4 inch ?
That is the only thing that will get rid of the tree roots. Hydro jetting will offer temporary relief but won't do a thing for tree roots. The problem is he has plastic corrigated pipe. The power snake will destroy that pipe.
Myself, I don't think he has a root problem with that pipe unless there is an opening for tree roots to enter.