re-reading the thread...
You are using "client-to-client" on the openvpn server.
This already handles the routing between clients, so packets won't touch your iptables rules shown above.
You can try without client-to-client , but then linux has to do the routing.
Make sure routing is enabled:
cat /proc/sys/net/ipv4/ip_forward
Output should be 1 .
and have p[roper iptables rules in p[lace