In this instance it's a Extreme managed switch, but I guess this would apply on others too.
Basically, I noticed we couldn't ping the switch, and eventually found this was down to the fact the switch itself didn't know where to route the packets in responding to the ping request.
Now I've add a static route for the monitoring network, but I'm wondering if I should add a default gateway as well, as one isn't currently set. However, if I add one will it effect the 'switched' traffic that is already travelling over the network normally, or is the gateway and routes defined on the switch only for the management traffic of the switch itself?