cannot find a command to import an esx image
You can't upload an ESXi image to Update Manager afaik.
But you can upgrade an ESXi node with with an Offline Bundle and the Install-VMHostPatch cmdlet.
See for example https://www.virtualizationhowto.com/2017/08/update-vmware-esxi-6-0-6-5-powercli/
Blog: lucd.info Twitter: @LucD22 Co-author PowerCLI Reference