but when the traceroute, still through eth0, instead of tun0
To where you make traceroute?
in Client1, routing to network 192.16.168.0 gw 10.8.0.6
192.16.168.0/24 route add-net 10.8.0.6 gw devtun0
You are adding this manually?
Show OpenVPN server and client configs and logs.