Is the interface enabled? I think by default the third interface needs to be specifically enabled by marking a box. what does it show if you go to "status", "interfaces"?
if what you are saying, is that you connected a switch directly to the OPT1 interface, and then connected your computer to that switch and put your computer in the same network as the OPT1 interface then yes, you should be able to ping the OPT1 interface. Actually, you may have to allow a firewall rule on the OPT1 interface because there aren't any setup by default on that interface. So make sure you allow ICMP to that interface too.