First, the purpose of the sacrament of penance is to receive absolution for post-baptismal sins committed. For a self-help group to attempt to use the sacrament for any other purpose (e.g. as simply
to fulfill one of the steps of a 12-step process) would seem to be inappropriate at best, if not at worst sliding along the path to sacrilege.
Second, only baptized persons can be validly admitted to the other sacraments, including Penance.
Third, those receiving the sacraments need to be properly disposed toward them and also educated in their purpose.
Finally, Canon 843:
§4. If the danger of death is present or if, in the judgment of the diocesan bishop or conference of bishops, some other grave necessity urges it, Catholic ministers administer these same sacraments [Penance is one of them, along with Eucharist and anointing of the sick] licitly also to other Christians not having full communion with the Catholic Church, who cannot approach a minister of their own community and who seek such on their own accord, provided that they manifest Catholic faith in respect to these sacraments and are properly disposed.
§5. For the cases mentioned in §§2, 3, and 4, the diocesan bishop or conference of bishops is not to issue general norms except after consultation at least with the local competent authority of the interested non-Catholic Church or community.
Notice the requirements:
1) Danger of death or other grave necessity (as determined by the diocesan bishop, not the minister)
2) The person must still be validly baptized
3) The person cannot approach a minister of their own community (pretty difficult to imagine, in the case of a 12-step program, which doesn't specify, IIRC, that the admission be made to a minister)
4) The person must manifest Catholic
faith in the sacrament and be properly disposed
In other words, sure, a Catholic struggling with addiction and properly disposed
(i.e. repentant and seeking absolution of all sins) may fulfill this step of the program by going to confession (and confessing all sins he is aware of, not just the sins associated with addiction), but not non-Catholics.