Yes, its a federal building where they take the test, so they are required to follow ADA codes.

The operative section of the ADA does not apply to Federal agencies.

Title I of the Americans with Disabilities Act of 1990 prohibits private employers, state and local governments, employment agencies and labor unions from discriminating against qualified individuals with disabilities in job application procedures, hiring, firing, advancement, compensation, job training, and other terms, conditions, and privileges of employment. The ADA covers employers with 15 or more employees, including state and local governments. It also applies to employment agencies and to labor organizations. The ADA's nondiscrimination standards also apply to federal sector employees under section 501 of the Rehabilitation Act, as amended, and its implementing rule.

In other words, if he was applying for a job at USCIS, USCIS would have to provide reasonable accommodation under the ADA. But the ADA doesn't apply to immigration tests/applications.