1. how to identify what are the drivers which are provided by VMware? and what are the drivers which are provided by hardware vendor?
this can be identified using powercli how: download your customized Zip file to your local hard disk where powercli installed then open power cli execute below command: Add-EsxSoftwareDepot d:\IBMCustomISO.zip then execute Get-EsxSoftwarePackage . It will list out all of the VMware drivers and Vendor Drivers
below is an example where I can see the drivers and vendor as well the driver versions
2) Do I do patching ESXI through update manager, will this update all drivers i mean hardware vendor driver and Vmware provided drivers?
It's depends but typically update manager will patch only related to VMware ESXi drivers and patches. but it can be also used to install and upgrade 1000V switch vem module and Powerpath softwares. how ever you cannot perform all the third party vendor software thru Update Manager. you need to perform thru esxcli software vib command
3) Do i need to update the image every time when hardware vendor released for new driver?
not necessary but it is best practice to have update to date version. the important this is you always need to check what is the compatible driver and software version at VMware HCL page and need to update accordingly.
Mostly no one will upgrade the hardware drivers all the time to up to date unless if there is some issues occure after patching ESXi due to non compatible. But It is always necessary to patch ESXI every month to avoid security vulnerability issues.