is it valid to have a kintype thats an alternate version of a greek god?

The concept of ‘validity’ as far as kintypes go is close to meaningless. Being kin is an internal experience that at the end of the day, effects no one but yourself and those you chose to share it with. 

That said, having a kintype that is a greek god of some kind makes as much sense as having a kintype that is a mythological animal, or a fictional character. A greek god has a mind, personal characteristics, and presumably a spiritual existence. Its not a vague idea, or an inanimate object. Furthermore, gods in mythology get incarnated as human beings fairly often. Its not out of the realm of possibility. 

Just remember to be sensitive about your identity. Remember that you are a mortal now, and you have to get along with mortals. Don’t go and tell people who may worship your god-identity how they should worship, and don’t try to gather worshipers for yourself. Other than that, you’re fine.