Great idea about pseudo VLAN - should be the solution. Will test it.
Considering VIP it's easy (be aware that at least on 11.5.3HF2 running as VA on VMWare just disabling VIP do not make it really dead - I can still ping VIP and access VS provided content! Only ARP disable seems to work reliably - don't know if it's only a case on VA and works OK on physical BIG-IP).
Regarding test pool, seems that one pool should be OK. Member will be gateway node with monitor for it's IP and second, third... transparent monitors for devices behind DG. With Availability Requirement set to All pool should go down in case DG stops responding or any of upstream devices stops responding - Am I right here?
Piotr