Maybe someone else could comment, but based off the symptoms provided (e.g. VIP cannot be pinged when Brocade is the Active VRRP device) this looks like a Brocade-specific issue. Is there any evidence that you found that could tell you this is an IE issue?
VRRP Active-Master failover seems to work fine so this means the Brocade and IE devices can listen to each other. I would be concerned if somehow, end devices, or switches downstream still believed that the way to reach the VRRP Master switch is still via the IE when it is Standby (not Master anymore), instead of the Brocade (e.g. some old VRRP MAC address still pointing to the wrong interface). You could try to take a packet capture on the incoming interface of the Brocade, to see if the pings are coming in.
Port mirroring and monitoring configuration
On the other hand, I wanted to share the Configuration Guide for FHRP for IE switches. It does not look like anything special is required to make them work with 3rd party devices.
Cisco Industrial Ethernet 4000, 4010 and 5000 Switch Software Configuration Guide
Hope this helps,
The fact that you cannot ping the virtual IP address (VIP) is implementation specific. On some implementations, like JunOS, you need to specifically enable the ability for the router to respond to pings to the VIP. According to the Brocade documentation, it looks like pinging the VIP is not supported.
Does pinging through the router works?