The gods of 7 Degrees of Freedom have no objection if you want to advertise your own MUD here.
The condition is that the advertisement policy at your MUD should not restrict advertising either. This is a very reasonable and fair policy.
You should honour the spirit of this policy, or it will be tightened up.
Note that if you are advertising, the policy on spam and harassment still very much apply.
See also: info mudlist.