One can use an H mount Phase back on an RZ with a Leaf adapter (we make one for our H backs) and either a Phase wake-up cable or a KG OneShot cable.
The Hasselblad H2/ H3 backs have a lever at the top that gets in the way. If you shave it off it'll fit on the Leaf adapter but you'll have to either shoot tethered or use an ImageBank
H mount Leaf backs work fine on ALL RZ models with the Leaf adapter and One lens-to-back sync cable.
Yair