I assume you have two networks Network A and Network B (lets say the printers are on Network B). Network A needs to use the printers on Network B using the VPN connection. I dont know anything about the bridged networks but i know that you just want two local networks to talk to each other (via VPN). The Server need to share it's local resources to the Client. But only share its local resources (LAN) and not using it as gateway (than you would use the VPN servers Internet connection).
This means that you need advertised routes so your client knows, HEY! This guy is trying to reach the 192.168.123.100 (the printer ip), ahh for that network i need to use the VPN (TAP interface). In Zentyall you can add advertised routes to at the client package (which you download) so the OpenVPN client application knows when to use the VPN and when not. In your case it only would be the 192.168.123.x network (where your printers are).
Just set up a VPN Server at Network B where the printers are, make sure the advertised routes are add... make sure the VPN Client (at Network A) connects to the server, than all the resources at Network B should be pingable and usable for Network A. IF you want interconnecting networks (routes are exchanged in both directions) you need to setup a site-to-side (zentyal-to-zentyal) network.
Configuration of a VPN server for interconnecting networkshttps://wiki.zentyal.org/wiki/En/3.5/Virtual_private_network_(VPN)_service_with_OpenVPN#Configuration_of_a_VPN_server_for_interconnecting_networks