CVE-2014-0224 is the only one that really impacts OpenVPN (No DTLS nor SSL_RELEASE_BUFFERS etc) and as others have said, if you are using OpenVPN chances are you are making use of TLS-AUTH which helps mitigate MITM issues to a reasonable degree. Furthermore, both sides apparently need to be vulnerable. So if you have little control over the clients, updating the server seems to be adequate to address this specific bug.