No, the DOJ has not posted any guidance regarding face mask usage in relation to the ADA.
The DOJ released the following statement denying issuance or endorsement of such guidance:
COVID-19 ALERT: Fraudulent Face Mask Flyers
The Department of Justice has been made aware of postings or flyers on the internet regarding the Americans with Disabilities Act (ADA) and the use of face masks due to the COVID-19 pandemic, many of which include the Department of Justice’s seal.
These postings were not issued by the Department and are not endorsed by the Department.
The Department urges the public not to rely on the information contained in these postings and to visit ADA.gov for ADA information issued by the Department.