1 - Grafdigger's Cage says "Creature cards in graveyards and libraries can't enter the battlefield.
Players can't cast spells from graveyards or libraries."
No part of that would stop God-Eternal Oketra's ability, as it A) is not 'cast', it is a trigger, and B) it doesn't make it enter the battlefield from the graveyard, just puts it back into the deck.
2 - God-Eternal Oketra's other effect says "Whenever you cast a creature spell, create a 4/4 black Zombie Warrior creature token with vigilance.", it has to be a 'creature spell', something which is 'cast'.
Cards that create creature tokens, like the bat card, and Oketra herself, are not 'casting a creature spell' when they produce tokens. Cards that can revive creatures from the graveyard, may be 'cast', but they are not an actual creature spell so these don't count either. If a creature in a graveyard has an ability that can put itself back into play, then this is an ability being played and not a spell being cast, once more this will not count. But if it does actually, specifically say it can be cast from the graveyard, then it would trigger Oketra to produce a 4/4 zombie.