They're the same god and pantheon, the Romans copy pasted the Greek religion and renamed everything. And GoW3 already fucked the chance at having both existing concurrently by having 'Hercules', the romanised version of the Greek hero Herakles be in the game as Zeus' spawn. He even wore a centurion themed outfit. (Also a joke about being voiced by Kevin Sorbo.) It was a careless thing to do even then, since in Ghost of Sparta, the first game after 3, you go to a place literally called Herakles Square, even though there's no Heracles in that universe. Whoops.