recently had this exact problem, you don't need the OOB port so just set its IP and gateway to something you'll never need (or just leave it un-configured completely make sure it's unplugged/disabled) what you did with the VLAN is correct you just need to set the gateway: console>enable console#configure console(config)#interface vlan 1 console(config-if)#ip address 192.168.0.250 255.255.255.0 console(config-if)# exit console(config)#ip default-gateway 192.168.0.1 by setting the default gateway you should now be able to administer your switch from other subnets you might have already worked this out, but good to leave it here for others.
sHello,  We have replaced on our old powerconnect 62xx with a new stack of N3000 switches.  With previous hardware there was no isolated management interface. As a result we were able to administrate the switch from our LAN subnet . If I set OOB interface in our LAN subnet then I cannot allocate IP to VLAN . ... .  How to be able to administrate our N3000 switch via web gui from our LAN subnet.   I have tried to setup ip address for vlan1 in the hope I would be able to web gui for management ...but no ...  console>enable console#configure console(config)#interface vlan 1 console(config-if)#ip address 192.168.0.250 255.255.255.0   Can you please help ?  Thanks for reading my post. Gmiga.  
N3000 web management interface from LAN