In the CHIP's case, I don't know, but AllWinner had a tendency to build drivers into the Linux kernel without providing source and use modified versions of various libraries while claiming to have developed them internally.
The Raspberry Pi machines use a family of Broadcom chips. These include some kind of general-purpose processor built into the GPU (sometimes called the VC4 or VPU). During operation, it runs an RTOS that handles OpenGL ES calls, translating them to QPU instructions. During boot, it's the first thing brought up; it initializes the RAM, loads the next level bootloader, then starts the ARM CPU. There's an open-source video driver that does the OpenGL work (and I think actually supports OpenGL, not just the ES variant). There's work being done on making a bootloader replacement, but it's in the fairly early stages (https://github.com/christinaa/rpi-open-firmware).
Maybe someone who knows about the CHIP itself will chime in with more detail on how it compares.