Is oral tobacco an aid for nicotine addicts like methadone for heroin addicts?

You have to draw the distinction between methadone and oral tobacco as (ostensible) harm reduction measures.  This is a critical distinction that makes all the difference between good public health policy and pandering to destructive corporate interests.

Methadone* is
1) chemically distinct from heroin, and
2) delivered in a medically controlled environment to patients receiving treatment to quit an addiction.

Oral tobacco is
1) the same as tobacco, and
2) delivered by tobacco companies in an environment these companies intend to be supportive of continued tobacco addiction.

The closest harm reduction equivalent of heroin to methadone is tobacco to NRT.  Even this is true only when NRT is used as an aid to total cessation only and not as an addiction maintenance mechanism.  For tobacco control to follow the harm reduction model of heroin, tobacco must be removed altogether from the harm reduction model, just as heroin is removed altogether from the heroin harm reduction model. 

*In addition, methadone therapy has an evidence base demonstrating efficacy in treating heroin addiction [e.g., here's the reference to a systematic review from the Cochrane database: Mattick, RP. Breen, C. Kimber, J. Davoli, M. Methadone maintenance therapy versus no opioid replacement therapy for opioid dependence. [Systematic Review] Cochrane Drugs and Alcohol Group Cochrane Database of Systematic Reviews. 2, 2008. AN: 00075320-100000000-01658]. Smokeless tobacco has no such evidence base as a treatment for smoking.