It will "work" as an IP camera without a VTH device - at least in
Blue Iris. I only use mine with Blue Iris, so not sure about
NVR (assuming you mean an appliance NVR).
You don't mention if you've already bought the VTO, but this is one of those areas - meaning video doorbells - where the
perfect device seems not to exist. Lots of discussions on power, wiring, chimes, functionality, phone apps, etc. as you
search the forum - with some remarkable solutions! And there is also something of a use case distinction between a video
doorbell and a video intercom. I have two VTO's and six VTH's and I selected the Dahua system because I wanted the
intercom functionality. If you want a video doorbell, with much better video specifications for example, and a better
phone app, etc. then the consensus on this forum is the Reolink doorbells.