The reason I asked this, I just went through the same situation where we had 4 nodes and upgraded to 5th node. In order to add it to the existing cluster EVC mode had to be turned off. I spent several hours with both Dell EMC and VMWare trying to turn EVC mode back on as well as following the same article you mentioned in your initial post and of course hitting the same roadblock. The way I got it enabled on both my sites was as follows:
1. Create an additional cluster with EVC mode enabled.
2. Moved the new 5th host which also was a newer model than the others.
3. Once I did this EVC mode was able to be turned on.
4. Moved the 5th node back into the original cluster.
My takeaway was that the nodes had to have the same instruction set in order to turn EVC mode on initially and since the odd man out was now in an EVC cluster vCenter could see and no longer had any "hidden" processor instructions.
NOTE: this required zero down time for us and I did not have to turn off a single VM.
I hope this helps! I spent many frustrated hours on calls and walking through KB articles for nothing!