Sorry to say but thats against EULA.
Not really, since the cubelets does not do anything towards in game and have no extra perks or advantage other than only being accessories, thus, not against the Eula
ADD
This is the part most people are having trouble understanding : "try to make money from anything we've made;"
This was made since a kid uses his grand ma credit card to buy a diamond sword in a server...
So yeah...
That is what they mean try to make money from anything they have made.
while the server was not made by mojang, but minecraft is, Thus the eula is bound to the server.
But since this server does not make people want to buy their rank by giving extreme advantage towards game
[Voting i believe does not count, since they does not give themself advantage, but just changing game mode]
As long as it is fair for everyone, it is "OK"
And since this is just for accessories, This would be just fine, as they does not gave in game advantage in any possible way.
k. night