You can hide the DLs from the address book no problem... you should be able to remove the SMTP address or change it if you want although I have not done this myself and would kind of question the need to do so.
If you remove the list you are setting yourself up for lost messages... not good. This is the DL where Unity sends messages from outside callers that cannot be delivered for whatever reason - you should have an admin type on this list (at least one) to handle these messages. If it's missing or moved then those messages just get lost.
