Specifically, I want to know if you can get a Hariyama that knows Whirlpool in SM. I know it must learn Whirlpool from HGSS, but it is an HM move in those games. I'm not sure if you can transfer it from HGSS to BW/B2W2 legitimately.
If you can't, then why does Pokemon Showdown say that Whirlpool is valid on Hariyama?
Thanks