two things to look at that totally stabilized my system...
1.) I moved the vcenter out of the cluster and put it in another vdatacenter and cluster. I know that this is not supposed to matter... but, ever since I did that, I have had 0 problems...
2.) are you using vlans? if so, you need a rule or it doesn't complete, much like you describe. You need a deploy rule that tell it what vlan to use on the mgmt interface when it is first booting as so: set deployoptions "vlan-id" 155 ...question I never figured out was how did it ever work at all int he first place as I didn't discover this rule until recently and I had problems, but then hosts did boot sometimes... then they would have a problem and not boot after.
also, if your host has ever booted into the cluster and you are rebuilding it, you have to remove it from the cluster when you rebuild it... I guess that is rule 3.
Let me know if any of those helped. My system is rock solid now that I got that all done... I'd like to find a job that I can use it in now! current place of work motto: if it aint broke don't fix it... :-(