I don't imagine that there are many integrators out there that use SNMP on a regular basis for two reasons: the initial barrier to entry that requires that an integrator learn about SNMP, its deployment and use, then comes actually configuring the monitor sets to get actionable information.
In my experience most people that try to deploy SNMP get an initial barrage of notifications from the network, and unless they are committed to putting the time and effort in to actually configuring what is being monitored / alerted it gets dropped relatively soon or just ignored. Yes I know, there are some platforms that reduce deployment, and configuration time required to get actionable information, but then this creates a third barrier - cost. There are very few integrators that I know of that charge for proactive maintenance of CCTV networks on a monthly basis (I don't know why, btw) so they would have to roll in the cost of setting up the SNMP system during the initial install (and choose a platform with no recurring costs).
I assumed that what I describe above was widely known by VMS manufacturers and that is why some have attempted to develop "health monitoring" functionality to provide integrators with notifications that they will actually care about: camera up/down, Gateway up/available, VMS server CPU/RAM/Network parameters within acceptable tolerances, etc. To make things simple for integrators.
Wasn't this Viakoo's, and other such platforms, business proposition?
SNMP is much more heavily used in the IT space then in physical security (given that most MSPs use these kinds of tools to monitor the environments they manage), but even there it take time to get it right. Most modern IT companies (specifically MSPs) will also be using multiple tools - SNMP + an RMM tool, or in our case (with Kaseya) an RMM tool that integrates SNMP functionality. Combining these tools allows for single pain of glass monitoring, maintenance, and remediation capabilities.
If you are a VMS manufacturer or a large enough integrator choosing a good RMM tool can do wonders for supporting IP based systems - couple that with a good documentation platforms (like ITGlue) and you can get a single support technician supporting hundreds of IP based access control and CCTV systems.