VRRP2 and VRRP3 are standard protocols and so the FB2900 can work alongside other devices that support VRRP2 or VRRP3.
Note that the FB2900 has non-standard support for some specific packets sent to the VRRP virtual addresses. This includes answering pings (configurable) and handling DNS traffic. Other VRRP devices may not operate in the same way and so may not work in the same way if they take over from the FireBrick.