There doesn't seem to be any point for Yao to train with Hakeem, Yao's already good in the post and in the D. Plus, Yao already had Thibs as his own personal trainer, Thibs may not be as famous as Hakeem but the work he did on Yao was pretty good. To me, Hakeem is best used working with guys who have mad athletic skills but lack the brains to use them properly in the post, or guys who need street cred before they listen. So guys like DH, Cousins, Bynum (if healthy), Josh Smith or guys like Kobe, LBJ.
Yao was light years ahead of Howard as far as a post player. If you remember Yao would dominated Howard and Houston would beat Orlando.