orry, I see you referred to same link as one I posted, apologies. And, yes, as @AkosBakos had said, you never know if issue would happen until you try it. I tested same process in the lab, worked fine. Think about it this way...
Say you are upgrading just one mgmt and say single gateway managed by it, from, ie R80.40 to R81.20. Technically, since thats major upgrade, it may load initial policy on the fw after reboot and then you need to install right policy and all works fine again.
Though, in your case, since its minor upgrade, I would be really surprised if you had SIC issue...I had done this in lab few times for mgmt HA, never had an issue.
One time, I did not even follow the steps, I simply went by logic as cluster HA, I upgraded standby mgmt member, which was also secondary, rebooted, then did active (which was primary) and all was fine.
Best,
Andy