iOS network connectivity on a local, isolated network with no DNS server
It's not a direct answer, but why not set up dnsmasq somewhere on your 192.168 network and use that hosts ip for the dns server in the ipad config? It should be a viable workaround. If this extra network doesn't have www connectivity, make an entry for apple.com in the /etc/hosts file where dnsmasq runs. This should trick the ipad to thinking it's truly online.