Have you found any development manual for the radio in the NXP OM15080? I was investigating that board before and it looks like a natural successor to the usb-kw41z, but it looked like the manual was missing all register descriptions and details for the transceiver components, only the high level description was kept. There is another variant of the same board named k32w which supports both Bluetooth and 802.15.4, similarly priced. Porting effort will probably require a fair amount of low level work because it looked like the peripherals are different than in the Kinetis MCUs.
Yea you are right - there is indeed no register definition for the radio on the K32W061.
I downloaded the SDK to see if there is any source code for the driver, but the whole 802.15.4 MAC is only available as a .a archive. 