FHD CDNG raw without window.

A lot of cameras (Blackmagic, Alexa, Red, etc.) window the camera when shooting in Raw at lower resolutions.

How do cameras like 5DmarkIII with Magic Lantern Raw and Hassleblad H6D-100C offer lower resolution raw video utilizing the full sensor? I thought this wasn't possible?

And from my own experience with the 5DIII I don't think it's any sort of line skipping because the aliasing is not that noticeable.

It is called pixel binning. The sensor has to support this and than you can combine sensels for a larger sensel.
The 5D MkIII has 5760x3840. By 3x3 pixel binning and 16:9 windowing you get 1920x1080.

Sony is doing that too in the F5/F55, but you need to change the OLPF to reduce moiré.

Would love to have that in the URSA Mini Pro !