What does your question about a small MUD have to do with a shell acount?
DreamHost doesn't offer running server programs like that. There is even a clause in the Terms of Service (TOS) that beings "The customer agrees to make use of DreamHost Web Hosting servers primarily for the purpose of hosting a website, and associated email functions." Not to mention the stipulation in another clause that says "Any application that listens for inbound network connections (even if the application would otherwise be allowed) are not permitted."
Besides that, this is a customer forum. There is no guarantee that you will get an official or valid answer to your question here. If a question about policy isn't answered in the TOS, contact sales at http://www.dreamhost.com/contact.cgi
Why exactly do you need a remote shell account to test a MUD anyways? As another forum visitor says, "There is no place like 127.0.0.1"