Just a quick note incase it helps anyone else out there.
I was recently in a lab moving from a vSS (Virtual Standard Switch) over to a vDS (Virtual distributed switch) when I came across and issue with a Pfsense box.
I had two VMs using CARP (which is like HSRP or VRRP) to push about a highly avalible IP address.
Now most vm admins out there will work out that for VRRP or CARP to work you need to enable "Promiscuous Mode" within the vSS or within the port group.
The issue I came across was with Promiscuous Mode and one uplink port (vDS or vSS) CARP was working perfectly however on adding the second uplink port to the vDS, pings to the CARP address were dropping.
Therefore - lesson learned was: When load balaning across multiple nics (or uplink ports in vDS terminology) you need to also be using the load balancing method of "Route Based on IP hash" (with accompanying switch config) if you plan to use CARP or VRRP else it will not work!