To be honest, neither Hexbear nor Lemmygrad has caused any noticable issues for lemm.ee. I recently compiled some stats for lemm.ee rule breakers by home instance, and as you can see in this post (in the “Administration” section), neither of those instances even made the top 10.

In general, mods haven’t complained about those two instances either, and the stats for community bans by independent community mods are more or less very similar. If any users creates issues in a lemm.ee community, then the community mods are free to just ban those users, regardless of what instance their account is hosted on.

if fact I wouldn’t even be able to as my home instance is defederated from these instances and thus such posts would be invisible to me

Preventing such situations for lemm.ee mods is actually one of the many reasons we don’t want to use defederation as a moderation tool on lemm.ee - we rather use site bans etc. Too much collateral damage with defederation, especially when dealing with larger instances which probably have vastly more innocent users than problematic ones. We reserve defederation for more extreme cases, like spam instances & CSAM.