Domaining aside... the two techs are very different, even in what the two companies are trying to achieve.
Using Oculus or VR would be similar to putting a full sized helmet on over your head and not being able to see the world around you. I can be standing directly next to you - but you would not be able to see me because you would have blinders on... a screen in front of you. While inside your helmet, you are seemingly taken away to a whole new world of your choosing... your mind is basically tricked into thinking that you are in this new world even though you would have never left the couch.
It has already been pointed out that the experience of VR will feel so real that the biggest worry is that someone with a bad heart can (and WILL most likely) die from the excitement it can cause. Example being sky diving. Someone with a bad heart can actually feel like they are really jumping out of a plane leading their heart beat to accelerate to the point of no return.
Think of VR as entertainment, gaming and a honestly, a drug.
HoloLens is really different from everything i just outlined in the fact that Microsoft (MS) is really just looking for a new way to interact with all the computing devices we already have and use... this is not meant to be an alternate world.
In comparison to above - HoloLens would be similar to putting a full sized helmet on over your head - BUT - it's completely clear and you never lose sight of the real world around you or the people in it. Instead, you are able to COMBINE the real world, with the functionality of the helmet, thus interacting with the real world around you AND the computer. It will combine both Augmented Reality and holographic technology seamlessly.
MS looks like they are aiming more for production and creativity than creating new virtual worlds like VR, although, would not be surprised to see these two bridged together somehow.
I would look at HoloLens as computing, productive, social, creative and business
As far as domains go?
... seems to me there are a lot of opportunities in future trends if you plan accordingly