Did you get this resolved? I'm getting the exact same issue on a server I had hoped to bring live. Wasn't expecting this roadblock.
Do you have an Esxi Essential license, what type of license are you using for vCenter 6.7?
I couldn't find a solution anywhere so just ended up rebuilding the server. Same media, same process, and I can create accounts on it this time around so I'm presuming I'll be able to join it to the vcenter server this time around as well (I won't be able to test this until this coming weekend).
If you could not create accounts on your previous installation, that would explain why it could not be added to vCenter Server - there is an account vpxuser which gets created as part of that process.
Now your new installation doesn’t have the account issue I suspect you would be fine adding the host to vCenter Server.