Look at the link I posted above the comment you just replied to. You can import an ISO(Such as your customized one) and add offline-bundles to it effectively allowing you to keep your version of ESXi up to date. I do it all the time.
I'm not sure what VEM is. Can you elaborate?
What you would do is:
1. Download the IBM or Dell customized CD
2. Use ESXi Customizer to implement whichever changes you desire(Updates, drivers, CIM...)
3. Out pops a customized ISO