There are more things that I don’t know about Haides that I wish I did than I can readily put in a post. One of them is whether at some point in the past the ancients did not view him as distinct from Zeus, but rather as a different aspect of his brother.
This question arises because of Haides also being called Zeus Cthonios (Zeus of the Underworld). We do not see a lot of recorded cultus specifically honoring Haides, despite the amount of cultus to Zeus. I wonder if the cultus was for both instead of only the one.