Thanks for getting in touch! It is definitely possible to use one server as two different environments - you will just need to add a second tentacle instance on Server B. Keep in mind that a single tentacle software installation can have multiple instances.
To set up a second instance, simply open up Octopus Tentacle Manager on Server B, then click on ADD NEW TENTACLE, and assign it a name, and a unique port to listen on (say 10934).
Once it’s all configured and started, simply add it as a new deployment target on the Octopus server (Infrastructure -> Deployment targets) like normal!