Are you aware of Farewell, vCenter Server for Windows - VMware vSphere Blog?
I' suggest you consider this, and go with the vCenter Server Appliance 6.5, to which you can migrate from your current vCenter Server 5.5, so that all settings are maintained.
Answers to your questions:
- No, hardware configurations are done by host, not by vCenter.
- No, WWNs for the hosts' FC adapters do not change, so there' no need for changing the presentation.
- If the FC HBAs are supported by the custom image (should be the case for HPE labeled HBAs) they should work after the upgrade, and since this is an upgrade, then multipath configuration shouldn't change.
- This may happen, if the image doesn't contain the required drivers.
- It's the hardware that needs to be supported. You can run the hosts with, or without a license during the evaluation period. A license however may be required if you need/request support from VMware.
- See my comment about the vCSA
Note: Keep in mind that HPE provides two different ESXi images, one for Pre-Gen9 hosts, and one for Gen9+ hosts!
André