Dual boot with RHEL 7.6 beta

I'm trying to do dual boot with CentOS 7.5 and RHEL 7.6 beta. I know there is a solution available[1], but it seems that the beta software is not working. I tried the procedure wit CentOS 7.5 and Fedora 28, and works fine. With Red Hat, it presents the CentOS prompt, but it tries to boot the Red Hat instead, and fails. I see that progress bar at the bottom of the screen. My /boot/grub2/grub.cfg is intact, that is, CentOS only.

The question is if this is because it's a beta version or is this really the way Red Hat is going to work?

Thanks for your attention.

Regards.

Marcelo
[1]
https://access.redhat.com/solutions/45409