I'm pretty sure the Aztecs understood their relationship to the gods as moral one, they just didn't construct it in Christian terms. Sacrifices could be a gift, establishing an obligation on the part of the recipient deity, or they could be the fulfilment of such an obligation on the part of the worshippers; sacrifice was thus part of a moral relationship. Just because it isn't assumed that the deity represents an iteration of the Good doesn't mean that the worshipper and deity do not act virtuously in relation to each other.
True enough, this indicates a moral system which precedes the deity and which the deity is located within (rather than one which the deity either creates or embodies), but it doesn't suggest a separation of morale and religious practice, as you seem to be arguing.