Worth noting as a disclaimer for people reading this: this is only true so long as external interfaces are not used. As soon as the BEAM calls out to other binaries, you lose that guarantee.
A disclaimer to the disclaimer is that you should be isolating that binary on dedicated nodes if there are stability concerns. Inter-node communication is trivial on the BEAM and it can be tweaked in the future when the scale of the system calls for it.
If you write an Erlang function in C you can actually call a function that lets the scheduler know you are willing to yield.