Feeling the vibration, yes. Seeing it, no. I'm not Deaf and I won't speak in their place, but a vibrating phone (that is not in the pocket) will not be noticeable. You won't always be attached to the desk where it's vibrating, so you won't always feel the phone.
A lot of Deaf people will probably appreciate this as an enhancement to quality of life. They'll probably be able to notice notifications more easily, especially if their device is at a distance. ... If I'm understanding it correctly, anyway.