I would recommend installing edirectory on all of the servers in the tree, and keep them all at the same level if you can help it. Get edirectory upgraded, and everything stable with it before upgrading zenworks.
What I remember from our upgrades to Zenworks 4, (we were still at ds version 7.x) and called Novell to make certain it would still work. The answer we got back is that there were features that may not work like inventory.
If you have policies, they will not upgrade well from zen2 to zen4-6.5, you will want to re-create them. Application objects should upgrade with little to no issues, and I don't remember about the inventory.
Good luck
TL