So, I thought the same thing, however, I was running into an issue with these 2 user accounts getting disconnected. I opened up a support ticket and they did confirm that the username has to be unique or the Session Limit count WILL affect the OnBoard user with the same name.
To work around this, either:
1. Increase the session limit count for the guest user to include enough sessions for both OnBoard and Guest connections simultaneously
2. Rename the guest user account
I went with option 2. Problem solved.
Thanks,
Rob.