[Libertas Omnium Maximus]

Can diplomats also join this?

So, this committee's membership is now fixed (see the second most recent host announcement on Pg 3 of this thread). That means that no-one new can join it. Why? Because we are just about wrapped here. What you can do, however, is join the olympics when the start in a couple of months. Diplomats are both given the opportunity and are encouraged to complete.