What would the "ethics" of a hive mind actually represent beyond slightly redundant flavour? What's the difference between a materialist or spiritualist hive mind beyond "one's a hive mind, but sciencey and the other's a hive mind, but mystical."
Very little difference, although the people of that spiritualist republic enemy of mine like them more, so they formed a defensive pact.
The "ethics" that really matters is pacifist/militarist, xenophile/phobe. Will this hive mind attack me? Does it want to be friends? What'll it think if I purge things? What'll it think if I enslave things? Will it help me stop another species from doing either of those things?
It'd be nice if by having long term friendly contact with a hive mind it could decide that maybe some aliens are nice, and it'd be nice if a bunch of empires attacking a hive mind could turn it into a flailing wounded beast intent on purging the galaxy. As it stands, so far, it looks like they'll all just be Hiveminds, responding as hiveminds do to the situation around them, never changing or evolving due to events in the galaxy, whereas with utopia we'll be gaining the ability to influence other empires through the galactic stage.
Of course we should wait to see how it is in game before passing judgement, but I dearly hope that they can have personalities beyond "is a hivemind". If not, we can always mod it of course.
And of course it's worth mentioning that just having them in the game is a major plus! I'll take the mechanics as is quite happily, they can always be expanded upon more later.