Hello, and welcome!
I'd like to help. Could you provide more info? This could be a routing issue, or this could be a packet forwarding issue, and I'd like to see if we can rule both out. If both of those possiblities are eliminated, it may be an OpenVPN configuration issue. I have not used OpenVPN in many, many years, so I won't be able to help with that. The VPNs I manage are either IPSec tunnels, or for some clients L2TP tunnels with IPSec transport (L2TP/IPSec).
You described that there is successful two-way interconnection between 10.8.0.1 and 10.7.1.2, but no success with 10.8.0.34 and 10.7.1.2.
- I could see this as a routing problem, if 10.8.0.34 and 10.8.0.1 are on different subnets. You have not described your netmasks for your 10.8 addresses, so this is a possibility -- the 10.9 device would need to have a routing table entry added to route to the second 10.8 subnet.
- I could see this as a packet forwarding problem, if you have not enabled the IPv4 packet forwarding sysctl on OpenBSD. This is easy to check; you would have edited /etc/sysctl.conf and uncommented the net.inet.ip.forwarding sysctl to set it to 1 on boot.