After reading their FAQ I think we should defederate.
Here's a snippet
Q: This is spam, can you stop?
A: First of all, I apologise for the inconvenience. All you have to do is block @bot@lemmit.online, and none of its posts will ever show up on your instance. If you you don’t want anyone else on your server to be exposed to this bot/instance, you should convince your admin to defederate from lemmit.online. Since there are no other users on here, there will be no harm done.
After reading their FAQ I think we should defederate.
Here's a snippet
No users to offend