Medicare G codes for substance abuse

Good afternoon Procentive Community,

I was just made aware of a G code that we could use to bill Medicare or bill Chemical dependency  services for clients that have Medicare advantage policies. I found the following two codes online :
G0396 (Alcohol and/or substance abuse structured screening and brief intervention services; 15 to 30 minutes) and G0397 (Alcohol and/or substance abuse structured screening and brief intervention services; greater than 30 minutes). I called Medicare and was told that the two codes were covered and there is no limit as to how often we are able to bill them. I would however like to know a little more about the two codes before I add them in procentive. Has anyone heard of the two codes? Do you use them often? Does the rendering provider need to be Medicare eligible? Do you use the two codes just for the assessment or for the individual and group sessions as well? If you only use them for the assessment what codes do you use for the individual/ group sessions afterwards?    

Thank you!