I suppose that is likely. However, prior to moving to Merlin version of the firmware, the stock Asus OpenVPN server did allow me to specify multiple user names and passwords on that same page. In fact, I had four unique users (each with their own passwords) all operating with the same .ovpn config client file generated by the router and imported into the client devices.
I'll be the first to admit that I have less than zero comprehension of the terminology and technology that makes it work. But, I really don't understand why the page shows a field for adding UN/PW with a limit of 32. I would have thought that if the per-user credentials are generated by the router during the certificate creation, those fields wouldn't be there, no?