I don't know if Earl has a mental health diagnosis and if he does I don't know what it is. I don't know if he takes meds or what they are so the effect of those meds cannot be predicted. It may be that proper meds would increase his ability to play well, that would depend on the condition and the meds.
I do know that he often acts immaturily and is guilty of letting his emotions often rule his actions. That's what emotionally immaturity is. He's unstable, often rude and anti-social. I would not want him, or anyone who does not control their emotions, acting in behalf of me in any personal or business situation.
For not knowing.....sounds like you just diagnosed him, Dr. Jim.
I somehow think he wouldn't be happy working for you anyway.