Anyway about your question, it's actually hard to say. It indeed has forms of dictatorship: Absolute power, ability to mute criticism. But on the other hand a group of people rule Cubecraft, and within that group they check and punish if everything goes correctly (no proof of this, but I assume it).
I do want to say one thing, and that is: There is only one administrator, he has too much power. I am not saying anything against Tacosbefriends, I am relatively new I don't have an opinion yet. But in my opinion it's bad to have only 1 administrator who plays such an important role.
I guess I do have to give an answer though, so I'll just go over your given examples (I stick to the definition you gave).
Monarchy: Hmm, the king/queen is Johncoles then? Can't really say anything about this, I don't know the influence of him inside the staff.
Democracy: Absolutely not.
Federation: This actually comes close to it, certain self-governing groups together. However this could still show forms of dictatorship if they form one ruling entity together.
Anarchy: Nahh
Dictatorship: Maybe. I think this comes the closest to Cubecraft (in combination with federation).
Now I do like to point out 1 thing: A dictatorship sounds really negative. However, to the purest form, it's just a government ruled by something that has the absolute power. In the Roman Republic there were 'good' dictators. As some of you might know, the usual form was: 2 consuls + senate. There could be chosen a dictator for one year if that was needed, mainly in times of war. These dictators had all the (mainly military) power, but they never abused it.
