Nope, not blocked. There's not actually that many of them, but they were one of the few established communities on Lemmy before the reddit explosion so I think they were disproportionately visible until everyone else started organically out-posting them.
I wish I personally could defederate from an instance while still using an account on a lemmy server. I've blocked at least a dozen communities from lemmygrad that showed up on my frontpage.
Its within connect, and they would probably be able to see your comments in a neutral instance. It is a temporary solution but I have been really pleased with it by blocking most porn only instances, at least its useful in that regard.
There was an issue on github asking for this but I dont know its status