There is a Deaflympics, which is sanctioned by the IOC. Per wikipedia, "To qualify for the games, athletes must have a hearing loss of at least 55 dB in their "better ear". Hearing aids, cochlear implants and the like are not allowed to be used in competition, to place all athletes on the same level."
Paralympics per Wikipedia, "The Paralympic Games or Paralympics, also known as the Games of the Paralympiad, is a periodic series of international multisport events involving athletes with a range of physical disabilities, including impaired muscle power and impaired passive range of movement, limb deficiency, leg length difference, short stature, hypertonia, ataxia, athetosis, vision impairment and intellectual impairment."
Going back to deaf volleyball, I was the head coach of volleyball there in 2010 and 2011 at the Oregon School for the Deaf (OSD), which plays sports in the lowest level of high school sports in the State of Oregon. "Lowest" level in the state of Oregon is for the number of students attending the high school. In Oregon there are six levels, 6A has at least 1000 students enrolled, while 1A has 74 student or less enrolled.
It is a unique environment as most of the students live on campus during the week (Sunday night to Friday afternoon) and return to their homes on the weekends. Some students do live in the town or their parents will drop them off everyday. This includes kids from elementary through high school in this environment. Because we were so small, we had the middle school and high school do things together, but usually focused on ball control, serving and spiking (from anywhere on the court). Also trying to get kids to read the ball (depth and pace) without being able to yell in out, deep, left, right was something that we had to teach and observe. I had one player who would be in the front row and get out of the way with a serve because she thought the ball was going back row, and it would land right where she started.
I've always wondered how deaf players signal each other in a team game. Not just volleyball but all team games. Do they require a different kind of referee?
I've seen deaf hockey at my university years ago, our uni team was out so they used the rink for practice. There wasn't really any significant difference as far as I could tell but I'm not much of a hockey enthusiast myself. The only thing I noticed was that their matches were a lot shorter than the usual 2 hr hockey game (intermissions included)