You shouldn't get a ban for this but you may get a warning for stating specific people's names.
Personally what I would do is put in a report. Copy/paste their quotes and whether SE will do anything or not we will find out.
However I think they do deserve a ban for exploiting 3rd party programs to get an unfair advantage.

What exactly did their 3rd party program do to make it possible for them to solo the S rank? I know that people are using teleport bots to get there instantly but they'd still most likely have other people come and assist.
I haven't seen any that make it possible to solo but I wouldn't doubt it. I remember people who used to exploit stuff back in 1.0 to be able to solo level 99 mobs without any chance of dying.