Yes, Theros gods can be commanders. They are Legendary Creatures and will be available as commanders after the Theros prerelease.
And yes, Daxos's ability can be used to cast cards outside of your commander's colors. This is because you're still not producing mana outside of your commander's colors - you're spending mana in your colors as though it were any color.
Vowels-Only Format Minimum deck size: 60 - Maximum number of identical cards: 4 Ban list: Cards whose English names begin with a consonant, Unglued and Unhinged cards, cards involving ante, Ancestral Recall