If I remember correctly, you can have only one default gateway for all your VMKernel ports. If you defined this default gateway once, this value is displayed on every VMKernel port configuration screen.
Have a look at the command line "esxcfg-route" to see what can be done.
Are you actually running ESXi? Classic ESX allowed you to have different default gateways on the Service Console and VMKernel interface, but ESXi doesn't allow this.
I removed it by using the CLI. It seemed to work flawlessly. Just make sure you make a backup of the file before changing it.
You can do a quick search by typing /gateway
Delete the IP inside of the brackets
/net/routes/kernel/gateway = "192.168.200.200" or whatever you IP is.
So when you are done, it should look something like this
# Deleted the IP address of the Gatway 1/30/2011
# who did it
:wq! to save and exit. Then, restart VMware with service mgmt-vmware restart which didn't seem to do one thing for me, so I moved the VM's off of the server, put it into maintenance mode and restarted the server. When it came back up. It was DEFINITELY now gone.