Is there a ATC protocol for dumping fuel? Or do they (ATC) just point the plane to a relatively quiet piece of airspace and keep the other traffic away whilst the pilots do loop the loops and barrel rolls with the gear down until they've burnt enough fuel?
ATC will send you off to a suitably quiet area - often over the sea if possible. Generally the plane will then be flown in a race track pattern while the fuel is dumped. It would not be normal to lower the gear or flaps.
All aircraft can land at maximum take-off weight though they would only do this in extremis - it carries an increased risk of a landing incident, but if the aircraft is on fire landing overweight will be the lesser of two evils. Aircraft that do not have a fuel jettison or dump system will have the ability to land at maximum weight if required, but again unless the nature of the emergency is pressing will burn fuel, sometimes by lowering the gear etc to increase drag.
A jumbo can take off at approximately 395 tonnes but has a normal maximun landing weight of 285 tonnes. Fuel jettisons at 2 tonnes an minute - approximately, though the rate will slow down toward the end of the fuel jettison.