Thanks @paul and @ahollifield for your feedback.  That gives me confidence in suggesting that option. The user experience in doing so it's so much better. It's really weird from Cisco ISE BU not to clarify the scenarios that they support or not, with...

Hi @paul  Did you had any confirmation from ISE BU regarding this scenario? That you never experience issues due never sending an "access-reject" to MAB use cases, when using dot1x/mab simultaneous on the switches? Regards, Fernando