In addiction counseling, it's appropriate for a counselor to disclose their history (or lack of history) with addiction when: 

they are in recovery from the same substance/behavior as a client, and listening to the client talk about their struggles with the substance/behavior triggers cravings for the counselor. 

they relapse and must inform a client about the relapse to model authenticity for the client. 

the disclosure can benefit the client and facilitate the counseling process. 

their work supervisor gives them permission to disclose their history with a client