|I haven't got a whole lot of experience working with VM's but from what I do have, I know two things.|
In the case of multiple subnets (VLAN's) you either need one Network Interface per network (VM) and one for the physical server itself, or, you need to make the Network Interface a "trunk port" and use a virtual switch in conjunction with the VM.
From what you've written, it sounds like you have an internal VM DHCP server and likely NAT capabilities built into the VM. What's wrong with using that? Why do you need an IP from your gateway instead?
If you have more than one NIC, then I suspect it would be easy enough to assign the second one to the VM and set it up to pick up an IP from your gateway and it's DHCP service.