As you say the scope is determined by the VLAN which is tagged on the network traffic.  First, let's look at ESXi. To have different virtual machines use different VLAN you have first go into the Configuration > Networking and make sure your "VirtualSwitch" is setup so that it has more than one "Virtual Machine" (this goes back to conversations about trunking on the physical network).  In our case lets say we have one Virtual Machine in our Virtual Switch named  "TEST" which is assigned a VLAN ID of 10  and other "PROD" which is assigned a VLAN ID of 11.   Now we go to any of our virtual machines on our ESXi server and change the Network Adapter > Network Connection Label settings to use either the TEST or PROD and depending on which it is set to the network interface on the ESXi server will "tags" the traffic with the VLAN you have setup in your Virtual Network and it will get passed across the network to the DHCP server (via helper) to get an IP address.

Same thing happends in View.....  When you setup your Desktop pool you will select a Default Image to use from your ESXi servers and when View generates desktops in the pool the network setting you had in the Default Image will be cloned to very desktop in the pool and which Vitrual Switch is being used and hence which VLAN is "TAGGED".   If you need a different vlan tagged on the desktops in a pool you must then use a different default image with the proper network settings.

Hope this helps but check out what "VLAN ID" you have setup on your Vitrual Swtichs in ESXi and I think it should fall into place for you.