DDWRT is ok, it can just be a pain in routing traffic correctly across site to site VPNs. It seems to always want to NAT things in that context.
I didn't notice the DDWRT routing table. That looks correct as well. The iptables rule should allow pings through.
Run a constant ping from the pfSense LAN to the DDWRT LAN. Go to Diag>Packet Capture, pick the OpenVPN interface, and start the capture. Let it run for a handful of seconds and stop it. If you see the pings leaving there, that'll confirm the issue's on the DDWRT side.
The only thing that'd prevent traffic from LAN getting routed across in that config is if you have a gateway specified on your LAN firewall rule(s), that'll force traffic to that gateway.