I use AS225r2 beta and armed with the knowledge that it should work I went on to try and configuring it. It took some trials, but I got it to work!!
First the gateway was "funny". It seems that it can be set in two places in the configuration files, but that does not appear to work. Neither does the ConfigInet the way I tried it. What does work is editing a line in the inet:s/start-inet where it says 'route add default ..'. Simply uncomment it and add the IP of the default gateway there.
Then dns requires adding a line to inet:s/inet.config which reads "usedns=true". Then inet:db/resolv.conf needs to be added with the name server(s).
After that I could ping time.google.com! However, name lookups are a bit slow and takes about 4 seconds every time. Using the IP number instead is instant.
The A3000 can almost warm reboot faster than doing a name server lookup...