It is unlikely that Allison Schmitt is completely deaf; she does not use the assistive technology accommodations typically afforded to deaf swimmers (ie. hand signals, special lights, etc) and a deaf interpreter is not observed during interviews. A web search found no verifiable reports of deafness.
Casual observers note a quality to Schmitt's speech and a uniqueness to her oral musculature that might suggest a hearing and/or speech deficit, though a web search suggests that Schmitt has not commented on this publicly and no verifiable reports were found.
Typical characteristics of hearing/speech impaired individuals may include the following: unusual flow or rhythm to speech, trouble forming sounds, difficulties with pitch, volume, or quality of the voice, trouble using some speech sounds, atypical oral musculature and more.