The Recurse Center's guideline against "subtle -isms" takes place in the context of offering financial aid only to favored groups. This suggests that "subtle -isms" against less-favored groups might be policed less vigorously. For example, many ordinary white men might reasonably consider the term "underrepresented" itself to be a "subtle -ism", but I doubt complaints to this effect would fall on sympathetic ears.
This issue applies to Hacker News because being inspired by the Recurse Center's policies risks importing the expectation that "avoid subtle -isms" mainly applies to speech against their favored groups. If Hacker News is to adopt Recurse Center–style community guidelines but wants to avoid such bias, it should be explicit in disclaiming any notion of "protected classes", instead insisting that the guidelines be applied equally to all groups.