It is really very odd. You are correct that if the 802.1p tag would make the traffic unavailable then it would affect communication with everything else, and not just the default gateway.
So the situation is that if you have the VM on a portgroup without Resource Allocation you can reach the gateway, but with this enable then communication stops? If you have a ping -t running will it just stop in the middle?
You have only a single vmnic connected to the Distributed Switch from each host?
