Out of the loop

No, they won't be able to. The way that it works is since lemmy.world is defederated, beehaw won't give or receive any information about changes made to their instance by lemmy.world users. When a different instance "visits" an outside instance like that they are really just creating a copy of the instance which is where the Lemmy.world users would be posting. Just like lemmy.world, any other instances, even ones we federate with, will create their own copy of beehaw's instance whenever they visit. The issue is that since we are defederated beehaw doesn't receive our updates therefore anyone going to beehaw to create their own copy won't see our updates to that instance either. The post that I linked explains it better I think but that's the gist anyway. Short answer, no, even if another instance federated with us they won't see it. They don't come to us to get the latest version of beehaw's community, they go to beehaw. And since beehaw doesn't let us update their version anyone who goes to them won't receive our updates either.