For an ArubaOS8 cluster you need a separate Mobility Master server. The cluster termology in the GUI without a Mobility Master is different.
When run two controllers without a Mobility Master you miss some features like clustering, live-updates, airmatch, etc.
Without a Mobility Master server and two controllers you still can create a master-standby setup as we did often in 6.x versions. In-fact you install two controllers in standalone mode and use the LMS IP settings for redunancy when a controller fail.
Still no need for VRRP :) ONLY for find the controller when a AP is not provisioned.
Example:
Option 43/60 and DNS aruba-master are set to the first controller. And LMS IP is set to the second controller. When an AP is not yet provisioned it connect to controller 1. While provisioned the AP get an LMS-IP of controller two, reboots and connect to controller two without using the DHCP options or DNS.
When controller 1 was down, the AP cant find the controller through option 43/60 or DNS and stuck in the boot process and reboot and reboot again. The AP never can be provisioned.
When option43/60 and DNS are set to the VRRP VIP and controller 1 is down, the AP discovery process reach controller 2 via the VIP address. Provioning take place and the LMS IP is write down in flash and is used by the AP to connect to that controller next time.
VRRP is only need when one controller is down and still can do a discover proces for new AP's that are not provisioned.