You absolutely can send the same stream to more than one recorder via unicast. Cameras in the office here are recorded by the building owner, who gives us access to them as well. In addition to their Genetec system, I'm recording one camera in two other VMSes right now while testing. No multicasting is involved.
The real issue with sending a stream to multiple VMSes/NVRs is how each handles stream settings. Some will simply take what's set on the camera. Others (Milestone and Genetec, especially) will push settings to the camera. So if you have an IP camera set to 720p 10 FPS, for example, and you've set it that way via web interface, then connect it to Genetec which is set to 720p30, the framerate will change on the camera as well, impacting anyone else who may be using that stream. It gets real interesting if you have multiple VMSes connected and they all try to push settings...
If you're using two Hikvision NVRs, though, and make sure that you configure them both the same, chances are adding the camera to both will work fine. I don't recommend this when we're talking enterprise systems with super high uptime requirements and multiple VMSes, but in this case you will probably be okay.