Without remediation he could begin to rely on bad decoding strategies (e.g., guessing based on context and the initial letter, identifying words by shape, etc.). Once these methods are set, they can be very difficult to break. And he's obviously got the ability to develop some of these alternate strategies.
His tutors should know how important it is to form a strong foundation in phonological awareness & effective decoding methods. If they don't seem to understand, then I'd seriously consider finding someone else.
