It is. Currently, the EULA is restricting everything unless the donation applies globally, not specifically to a player, or if it is cosmetic and changes no gameplay whatsoever.
And considering WE gives advantages, in the case of a competition, to build way faster, it's against the EULA.
Giving donors such privileges would most likely be against the EULA since it isn't fair to non-donors and such.
Then again I didn't really care to read about the EULA... but that should be the case.
It's one basic rule, you can't make a profit out of what Mojang made, wether it is an ingame item or a modified client. In the case of items, it's as far as it doesn't give an advantage or changes gameplay drastically for the donator.