The idea behind a VLAN is isolation. On the same Hyper-V Server, the two clients in question would have to connected to the same virtual network to communicate. This defeats the purpose of this question.
I set up two different VMs on 2 different Hyper-V Servers. Both were placed on external Virtual Networks and were able to PING each other. On one of the virtual networks, I enabled VLAN with an ID of 2. I also enabled it in the settings of the VM. Once this change took effect, the two VMs lost communication with each other.
In conclusion, the VLAN also isolates, as it should, communication between clients for both the virtual and physical worlds. Therefore, no RDP traffic can pass between them.