I've had good results using non Lorex IP POE cameras on several Lorex NVRs over the last few years. But, not everything ONVIF compliant works all the time. Overall I've had good luck getting most ONVIF and some non onvif cameras to work on various Lorex NVRs... MOST of the time, they are Dahua or Dahua OEM rebranded cameras however. I have had others work as well, at least at basic functional level - but not everything works as expected. IE, cameras may support 3 streams, whereas Lorex NVRs only support dual stream (D1 & high def). Other settings such as image adjustments may not work, or work as intended. The biggest nuissance I found was altering on screen text (time/date/ID etc).. Often the Lorex NVR will not remove any OSD text configurations set up on another brand NVR. Requires logging into the camera web gui directly, using Internet Explorer browser, then alter camera settings there. Kind of a pain, but once done, usually don't need to change very often. You may need to log into the camera directly before connecting to the NVR, in order to change port and IP assignments. Lorex defaults to different ports than other OEMs, and some cameras expect web access over a different port than the standart http:80. I have some non Lorex IP cameras working fine on Lorex NVRs for several years. Some were an absolute bear with much tweaking needed to give acceptable results; others were almost plug-n-play. Tried some older Hikvision 4mp cams on 2 different current model Lorex NVRs.. Nope, wouldn't talk to them at all. Had to run SDAP on cameras, reconfigure the cams to match Lorex config, then they worked ok.
So, hard to say.. it's a roll of the dice. As mentioned by others, Lorex is Dahua OEM - but they have MANY different versions, with differing firmware. Never know what will work and what won't.
I installed an LNR600 series system for a client back several years ago. It worked ok once set up, but it seemed to have issues with firmware and the Lorex app not communicating well remotely at times. If I recall, it was 4K, NOT 4mp as Lorex's own literature contradicts itself... BUT, the 4K frame rate was really low, something like 15 fps max, with limited camera subnet bandwidth - so forget running all 4k cameras. It worked ok at 4mp, however. Overall, I've found Lorex NVRs to be fairly reliable, and not hard to configure... but there is a huge disparity in firmware across the models, even within some model series. Even today, Lorex has various models requiring different (non compatible) Lorex apps.. which is silly. They also limit you to 3 concurrent online users on most Lorex NVRs. The hardware is usually decent.. but Lorex firmware can be aggravating and quirky.
