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.
Yes. God creatures are legendary enchantment creature objects in all zones, including the battlefield (of course, assuming the proper devotion has been reached).
and can Daxos of Meletis last ability be used if the exiled card is outside your commander colors?
Yes, it can. The colorless mana EDH rule applies only to adding mana into mana pools; it doesn't affect whether or not a player can spend mana as though it were mana of any color.
Private Mod Note
Rollback Post to RevisionRollBack
How to use card tags (please use them for everybody's sanity)
[c]Lightning Bolt[/c] -> Lightning Bolt
[c=Lightning Bolt]Apple Pie[/c] -> Apple Pie
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