vSphere supported upgrade sequence states that VDP needs to be upgraded after vCenter. Does VMware not support upgrades if your running VDP 6 on vCenter 5.5 and then you need to upgrade vCenter?
I can say from experience that in our lab we had vCenter 5.5 U2 and VDP 5.8. We upgraded vCenter to 6.0 before upgrading VDP to 6 and ran into issues. I had to switch SSO from vCenter to PSC and re-register the web plugin. I haven't done any vCenter 5.5 - VDP 6 upgrades yet but I suspect similar results. I have a lot of customers wanting to take advantage of the now free features of VDPA in VDP 6 but not upgrade vCenter to version 6 until update 1. Would it be considered better to build new vCenter instead of upgrade if VDP 6 is being used with vCenter 5.5?