I don't really think this will make a difference, but try disabling the explicit override of the port group to reject promiscuous mode. It should inherit the reject from the vSwitch level already.
Did you take a look at the vmkernel log as I mentioned too?
And you're not using VLAN ID 4095 on this port group by chance, right?
Also, you're not doing anything fancy networking wise in those VMs, right? In tcpdump, check that the actual destination MAC (-e for ethernet header) is not it's own or some broadcast/multicast bit set MAC too.