We don't run samba on our OpenVPN server, but it sounds like the VPN config is sound. You might try adding the interfaces = param and hosts allow = param to your smb.conf and see if that would fix it.
Assuming your OpenPVN server VPN IP is 10.0.0.254, and our VPN clients get an address from 10.0.0.0/24 the entries would look like:
interfaces = 192.168.x.x(LAN IP of samba server), 10.0.0.254(VPN server IP)
hosts allow = 192.168.x., 10.