Formerly chapo.chat and r/chapotraphouse, they are a tankie instance that frequently brigades threads that mention them, and engage in harassment campaign against anyone who disagrees with them. They also frequently praise and defend Russia and China, two genocidal dictatorships in which one is engaging in an illegal war against ukraine and china has rampant human rights abuses. Since there are good faith users on that instance, they are more of a hesitation than a censure.
Other way around. If they defederate from Hexbear, they will not be able to see Hexbear posts, but as long as Hexbear remains federated with OP’s instance, Hexbear users will be able to see the posts. Federation is a one way street.