This is a situation where circumvention is necessary - this is the route I would take in order to avoid having to stop selling ranks:
It's possible to make donations be out of love for the server and nothing else - with the underlying reason being, obviously, for money. However, simply state that because they donated, they get perks added on out of gratefulness. Essentially, it's not donating that gets you the perks but MeepCraft being thankful for you donating.
Not entirely sure if there is a part of the EULA relating to not being able to donate to servers at all. I won't go too deep into it currently, just my thoughts.
