The ADA prohibits discrimination in all employment practices, including job application procedures, hiring, firing, advancement, compensation, training, and other terms, conditions, and privileges of employment. It applies to recruitment, advertising, tenure, layoff, leave, fringe benefits, and all other employment-related activities.
Sounds clear to me.
So, who is covered (same link):
Employment discrimination is prohibited against "qualified individuals with disabilities." This includes applicants for employment and employees. An individual is considered to have a "disability" if s/he has a physical or mental impairment that substantially limits one or more major life activities, has a record of such an impairment, or is regarded as having such an impairment. Persons discriminated against because they have a known association or relationship with an individual with a disability also are protected.
The last sentence is crucial.....