Well, according to the specs that can be found on Wikipedia, a GWC needs to support at least spec 2 in order to be able to serve different networks. A problem you might have is that Gnucleus may mix gnutella and G2 IPs from time to time because it is not fully compatible...

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</td><td><a href="http://crawler.trillinux.org"><img align="right" style="border:0" src="http://crawler.trillinux.org/img/netsize.png" alt="Network size"></a></td></table>