It's part of the default install on my N5200 - Thecus call it nsync, but it's just openvpn.
On my N5200, the binary is installed as /opt/bin/openvpn, and the config files are in /img/bin/openvpn/. There's nothing to stop you restarting it with a different config that suits you though - just start with openvpn --config <file>. This is the version:-
# /opt/bin/openvpn --version OpenVPN 2.0.7 i686-pc-linux [SSL] [LZO] built on Jun 29 2006 Developed by James Yonan Copyright (C) 2002-2005 OpenVPN Solutions LLC <email@example.com>