Board Thread:General Discussion/@comment-25926288-20160509005929/@comment-25375217-20160511164140

Given that Hook deserved the ambrosia, did help at least somewhat in the final battle (Zelena probably wouldn't have stabbed Hades if she hadn't known it would kill him, she would have broken the crystal or taken it away or something), and also was apparently the price for Robin's life being saved (I love that theory btw!) and Robin was now dead, I'd say Hook's resurrection was deserved.

Zeus never told Hook why, Hook speculated. So we can't say that it's definitely his assistance, particularly with two other theories that actually kinda make sense.