You can use software / service like Check my camera which is an external test to verify the functionality of your CCTV Software and Hardware.
Though its currently not supporting the VMS you asked about...
Milestobe has built in reporting/alerting that can be configured in the Expert level and above. The lower level versions have similar, though more limited features. From Enterprise on down there is a free Dashboard program through Milestone. The Milestone Dashboard tends to generate far too many false alerts but the developers have been slowly improving it. I imagine the other VMS mentioned have similar features. It Boils down to a question of how difficult/time consuming they are to setup vs how much time you have to sink into the project and the value of assured recording.
It is very difficult task to confirm that. We have heard that many companies hire dedicate persons running playback from time to time.
The cause can be complicated, ranging from software configuration (motion detection threshold too high), system issues (file system, or database issue), to software bugs.
The only reliable way is to check and track the presence of the video files.
*Disclosure: I am a Genetec employee*
Genetec Security Center offers a very easy way to accomplish exactly what you describe: using the "System Status" task, you can actually see, in real time (and dynamically, so the status of a camera can change while the report is opened) if a camera is online/offline and recording/not recording. The list of cameras can also be sorted, i.e. show all non-recording cameras first.
This report could also saved and sent to anyone in the organization in the form of a CSV, XLS of PDF file. The report can also be used to see the live status of servers, doors, access control units, elevators, intrusion area and much more.
You can also create live actions (pop-up message, email, alarm, etc) when a camera event happens (motion, input/output, no signal, etc).
Let me know if you'd like more information, I'll be glad to help.
There are two aspects for this question: Detecting the missing video and preventing the missing video.
Questions like "get alert from VMS tells us that this camera is not recorded for more than 24hrs" is very interesting, it actually goes beyond that. What happens if the video files got deleted for some reasons? You though you have 30 days of video retention, how do you know for sure?
Having all the relative evidences is critical for finding out what casued missing video so that you can fix it. Is camera alive at the time? Is camera flapping? how about your camera network health? storage health? file system corruption? Any configuration changed at the time such as driver/software updating?