You can tell Zeroshell DNS to forward requests to another DNS server or servers for any domain, and I believe this includes anything in in-addr.arpa, which is the reverse DNS domain for IPv4 addresses.
If you want to forward requests to, say, 1.168.192.in-addr.arpa (192.168.1.0/24) to another set of DNS servers, click the Forwarders link in ZS DNS and add 1.168.192.in-addr.arpa to the list specifying the DNS server(s) that host the rDNS zone. You can do this for more than one rDNS zone.
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