I don't think zombie can operate without a head.
not to mention that Roger's body probably wasn't all that amazing. his telephatic abilities (he had those, right?) and Hakki (most likely he had) are all mental stuff. even if he had an amazing ability (devil fruit, though it's not likely), we don't know if they stay with the body after death.

and don't forget Moria was probably less than 20 when it happened, and didn't have the fruit ability, or the logistical means to get it.