I just upgraded our vCenter Server to 6.5U2 from 5.5. It went smoothly, even as it was a migration from a Windows vCenter Server to the appliance. I'm now trying to get the hosts up to 6.5 to match. We have HP DL380p Gen8 servers running ESXi 5.5, and I downloaded the HPE ESXi 6.5U2 (Build 9298722, which is the last pre-Gen9 version available) from VMware (via HPE's website), which shows as compatible on the HCL with our configuration. I uploaded the image to Update Manager, created a baseline from it and scanned for Patches and Upgrades. It came back as 'Incompatible' for all three hosts. Why? I was under the impression that you could go from 5.5 to 6.5 as long as the hardware was compatible.
After digging deeper, I found the following information on the host Update Manager tab but will need some advice on how to properly do this as I'm unfamiliar with modifying/removing/adding VIBs:
VMware ESXi 6.5.0 Update 2
Hewlett Packard Enterprise
The upgrade contains the following set of conflicting VIBs: