OK I managed to get the EZVIZ camera connected, via Wifi, to my HIK-Connect account.
1) Setup a separate EZVIZ account
2) Add the camera to that account, going though the Wifi Setup
3) Once it is on the network, I checked with the Hikvision SADP tool that it is indeed picked up and seen as a Hikvision camera.
4) Delete it from the EZVIZ account. It should keep the Wifi credentials in the camera (checked on my router that it stayed connected).
5) Add it to HIKConnect by scanning the barcode. In my case it just immediately added the camera to my account. If this didn't work, I would try to add it as "Connected via ethernet" instead of doing the Wifi setup again.
I'm now able to view it remotely without any issues in the Hik Connect app. Additionally, it seems to support many of the same features as it did in the original EZVIZ app.
Futhermore, I discovered that it also has a substream, which is useful if you want to record say 24h at a lower resolution. In the EZVIZ C3W case that I'm testing, the main stream is:
rtsp://admin:<verification code>@<IP or host>:554/H.264
or rtsp://admin:<verification code>@<IP or host>:554/Streaming/Channels/101
(1920 x 1080px, 15 fps)
While the substream is
rtsp://admin:<verification code>@<IP or host>:554/Streaming/Channels/102
(768 × 432px, 10 fps)