Do you have any other interfaces to other server monitoring systems such as Nagios?
We would look at that and implement something similar for Zabbix.
The API is fairly straightforward to query from Powershell, especially for ad hoc state information. Deep inspection (details of pieces of the configuration of complex tasks, or trying to access information Visualcron stores encrypted) is less straightforward, but the way Powershell interacts with Visualcron makes most things that are available fairly discoverable if one keeps wondering "what's under this next property?"
The service also records some things to the Windows Event Log or to log files.
There are also several kinds of tasks and notifications that can provide information worth monitoring, but especially when working with a central monitoring solution, it may not be desirable to rely on the service functioning as expected to inform you whether or not the service is functioning as expected (this is something I'm trying to find time to address more thoroughly, myself).
I am much less familiar with the capabilities of VCCommand (which I think of as a slightly less intimidating wrapper around a miniscule subset of what I can do with Powershell), accessing the .Net API through means other than powershell (mainly because of the conclusions in this
post), or the web API (for a few reasons - the most prominent being that I learned to use powershell first, but I also suspect it's less powerful, and for my purposes it's only a serious alternative if I can use a Visualcron credential with it (which I'm not sure I can't do, but I haven't figured out how I can).