Why do you need a physical nic to connect VMs? think of your vswitch as just a normal switch with the physical nic just being a connection to the real world switch.
All your VMs can talk as long as they are connected to the same vswitch, or if there is a router connected between the vswitches - pfsense with a vnic in connected to each switch. As long as one of the legs as tied to real world with physical nic, then even the physical world can connect to the virtual connected only vms via pfsense.
I wouldn't worry too much about the discovered IP ranges. Kind of a useless feature if you ask me ;) But it determines it by broadcast
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006744
If you don't have cdp or llmr switch you could do this to get it set how you want it to your network, etc..
http://sostechblog.com/2012/08/13/vsphere5-setting-the-observed-ip-range/
So back to your physical nic - do you have boxes that you want in this DMZ that are physical? If not then why do have physical nic on that vswitch? See my w7 box there in my dmz..
I can ping it from my lan segment from a physical machine
C:\>ipconfig
Windows IP Configuration
Ethernet adapter Local:
Connection-specific DNS Suffix . :
IPv4 Address. . . . . . . . . . . : 192.168.1.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.253
C:\>ping w7x64-vm
Pinging w7x64-vm.local.lan [192.168.3.206] with 32 bytes of data:
Reply from 192.168.3.206: bytes=32 time=1ms TTL=127
Reply from 192.168.3.206: bytes=32 time=6ms TTL=127
Reply from 192.168.3.206: bytes=32 time<1ms TTL=127
Reply from 192.168.3.206: bytes=32 time=1ms TTL=127
Ping statistics for 192.168.3.206:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 6ms, Average = 2ms
C:\>tracert w7x64-vm
Tracing route to w7x64-vm.local.lan [192.168.3.206]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms pfsense.local.lan [192.168.1.253]
2 <1 ms <1 ms <1 ms W7X64-VM.local.lan [192.168.3.206]
And it can talk to the internet - but it can not talk to my other segments because I have that blocked.
If you don't have a need for a physical devices to be on a specific segment you don't need a physical nic on it. Which you could then prob put lan on its own vs sharing with your vmkern