I can confirm that I’ve reported several spam accounts that were doing nothing but post links to their Amazon Affiliate sites. Reporting definitely does some good, in my experience, but I guess it depends on the instance admins.
The person I reported was on Kbin: Jumper74, Jumper75, and then Jumper76, and there’s probably a Jumper77 now too, who knows?
Sadly, I don’t think kbin themselves took any action, and I’m not even sure they were able to see my reports.