Same question; we are currently running the latest ESXi 7.0.3 Build 20842708.
Originally installed using the customized HPE ESXi ISO, always updated using Baselines.
Now wanting to switch to the image based method, as baselines are marked as deprecated in 8.0+.
Our cluster has 17 hosts right now, DRS and HA is enabled. We cannot afford to lose HA availibility due to removed vsphere-fdm.
Building the image using the latest ESXi Release (7.0 U3i - 20842708), adding the HPE Customization for HPE Servers in its latest release (703.0.0.11.1.0-25), additionally replacing the VMware-VM-Tools component with the latest async release in the Host-Image, so that 12.1.0 will be replaced with 12.1.5.

When I check the compliance, everything looks fine BUT the removal of 'vsphere-fdm' scares me, so right now I don't finish the process of setting up the image based process, as there is no way back to using baselines once the switch is made.
I read a lot of documentation from docs.vmware.com, I searched a lot of third party sites, but I didn't find an answer to this question.
After switching to image based updating, when the vsphere-fdm gets removed: will it get reinstalled once the host is updated with the newly created image? Another question: even IF it works this way, will the host still be "compliant" with the image after vsphere-fdm got re-installed? Or will it report a mismatch, because there would be an additional package installed which is not part of the manually defined image?
Some clarification would be nice. Thanks in advance!