My platform below:
3 x ESXi Host server v6.7 Update 01 (Cluster enabled)
I migrate out all running vm to other host, then I using Update Manager to update the ESXi host server form ESXi v6.7 Update 01 to 03, it is no prompt for ESXi host restart, and the build already updated show in vCenter.
So, may I ask using Update Manager to patch ESXi host server, does it need restart the ESXi server?
Every VIB contains a flag if Reboot is required or not. So it depends on how many VIBs (Patches) you try to installed and if its more a core component or just a 3rd party plugin like Dell OMSA for example. Murphys law will show you that always a reboot is needed and that will triggert by VUM.