Harvest can be made to work with the GN server with some moderate effort by editing the source code. GN requires that all CGI programs begin with the string /CGI. Below is a partial list of files where you will need to change /Harvest/cgi-bin/ to /CGI/Harvest/cgi-bin/.
src/broker/WWW/BrokerQuery.pl
src/broker/WWW/BrokerQuery.cf
src/broker/WWW/HarvestGather
src/broker/example/brokers/skeleton/admin/admin.html.in
src/broker/example/brokers/skeleton/query-glimpse.html.in
src/broker/example/brokers/skeleton/query-wais.html.in
src/broker/example/brokers/soifhelp.html
src/Harvest
Also, you'll need to make a symbolic link for Harvest. e.g.:
% cd /your/root/data/dir
% ln -s $HARVEST_HOME Harvest