It's precisely the reason dark matter tends to not fall into black holes. If you put a particle into an orbit around a black hole, it will basically do so forev

It's precisely the reason dark matter tends to not fall into black holes. If you put a particle into an orbit around a black hole, it will basically do so forever as it needs to lose an enormous amount of energy to drop down to a low enough orbit. Normal matter bumps into other normal matter when orbiting a black hole, heats up, and radiates away it's energy. This effect is most visible in the accretion disk of a black hole. But dark matter can still fall into a black hole and it still tends to concentrate due to gravitational interactions. If a dark matter particle is on a path unlucky enough to intercept the event horizon, it will of course not orbit. Also, gravitational interactions between dark matter particles or just normal matter can cause an exchange of energy, with one of the particles losing energy. Oh, and if dark matter falls into a black hole, it just makes the black hole a little bigger. There's no way to externally tell that the black hole contains dark matter.