Any real time application has to take the necessary short-cuts to render things in real time. That being said, there is a lot of technical wizardry you can learn to get some astoundingly good looking real time renders. But a game engine fundamentally cannot spend minutes calculating hair particle positions and volumetric lighting data for a single frame. It only gets 1/60th part of a second to do its calculations. It simply isn’t possible in that amount of time to calculate a simulation of all the physics and optics that are happening in the real world, but again, you can get some pretty believable approximations if you know what you’re doing.
The application you’re using doesn’t alter that, be it Blender or Unity or any other game engine. What specifically you could get away with would depend entirely on the nature of the scene, so there isn’t a definite answer to the question. You certainly can render creatures with fur in a game engine, and you can do it well, but not as precisely as you could do it if you were giving cycles hours of render time to calculate everything.
