Quite possibly the Cisco is set just to nat/route, though usually most routers do some form of DNS themselves on the basis they do DHCP for a network. Depends on how it has been configured.
Personally I'd ignore it and let SME do your DHCP + DNS (depending how SME & the Cisco are configured)
I usually set my routers as static or pass through and ignore them and let SME do the work.
If you really want SME to use upstream servers for external DNS then use the contrib. Makes it easier and you can swap to your hearts content
Unless you have a real strong reason to use Gobble you could use opendns for upstream.
Personally I hate giving any more info than necessary to Gobble etc. They have enough power & control as it is.
Back to Blighty tomorrow... balmy Bolton then bloody Burnham. Hear it's a tad warm over there