drheim - in my case I didn't realize there was a problem with the 1.98 FW that originally was published in SPP201903 until I remediate my vSAN cluster via VUM and found that the updates moved me to 6.7u2, oops. Fortunately everything seemed to work ok on the vSAN without issue. I had a persistent error in vSAN health about the controller firmware not being certified.
So as far as order... depends on where you are in your versioning. In my experience, one of the problems doing the controller FW first is the controller driver may fail due to compatibility issues where newer drivers are more apt to be backward compatible to older FW. Because it was vSAN I updated the controller FW one host at a time via iLO Repository while in Maintenance Mode. When it comes to updating my vSAN I find I can only hold my breath for so long :smileywink:
My 2 cents, your mileage may vary.