Moving to a dummy standard vswitch before moving is definately the way to go. Got esxi 5.5u2
still get the verification that "VM network doesn't exist" on the target, but clearly the code for migration has the correct error checking to ignore that, whereas the code for disrtibuted switches hasn't.
apparently someone in vmware forgot that if (like us) you go totally distributed vswitch, normal things like moving VMs around still happen.
P