Well, this is a very interesting situation and thank you immensely for sharing this with the community.
From my personal stand point, I don’t see any issue with a deaf / hearing impaired pilot in GA at all, or even in commercial aviation with a pilot/co-pilot. There are multiple systems in place these days, including ADS-B, that assists aviators in collision avoidance, traffic detection, ATC instructions and other issues that can arise from a pilot being distracted, deaf or any of the plethora of reasons for a pilot to not be fully aware and cognizant of the situation. Although a lot of GA aircraft do not have ADS-B since it is not currently required until 2020 and only if the aircraft is operating in certain airspace:
Class A, B, and C airspace.
Class E airspace within the 48 contiguous states and the District of Columbia at and above 10,000 feet MSL, excluding the airspace at and below 2,500 feet above the surface.
Class E airspace at and above 3,000 feet MSL over the Gulf of Mexico from the coastline of the United States out to 12 nautical miles.
Around those airports identified in 14 CFR part 91, Appendix D
All of this being pointed out, I think that being deaf or hearing impaired is fine for a GA pilot or for even a commercial pilot under the right circumstances. There are so many advances in safety systems these days that I can’t imagine not having pilots with impairments taking to the skies every day.