Apple doesn't actively lock and act hostile towards the reverse engineering folks. They just do their thing and sometimes do small jests to allow these folks to boot anything they want and play with the hardware.
...and while they're standing away from GPL stuff, they do have a dedicated site for Open Source software: https://opensource.apple.com/
...and while they're standing away from GPL stuff, they do have a dedicated site for Open Source software: https://opensource.apple.com/
Go to releases, and see what they do there.