i have a 3 Fujitsu servers, where is instaled VMware ESXi, 6.0.0, 3073146 - (Updated) Fujitsu-VMvisor-Installer-5.5.0-1331820-v300-2a , so is better way to update to latest build with https://my.vmware.com/group/vmware/details?productId=491&downloadGroup=OEM-ESXI60U2-FUJITSU ? ( Fujitsu Custom Image for VMware ESXi 6.0 U2 Offline Bundle ) or simple download latest build directly from vmware patch site ? (https://my.vmware.com/group/vmware/patch ) latest build -5050593 and update it ?
the latest Fujitsu image is here https://my.vmware.com/group/vmware/details?downloadGroup=OEM-ESXI65-FUJITSU&productId=614
You are best to keep with the custom ISOs because drivers/vibs may have also been updated (assuming your server is supported).