OpenVPN without NAT
OpenVPN server will function perfectly with or without NAT/PAT. The problem lies with the machines receiving the packets from 10.1.1.0/24 subnet; they do not know how to reply to as they do not have a route for it (and each machine software firewall may also need to allow the 10.1.1.0/24 subnet specifically).
Add a static route on the destination machines for the 10.1.1.0/24 subnet.