Most actions federate, any exceptions which aren't federated yet are generally just there because the federation logic has not been implemented (but improvements are constantly being worked on).
Generally federating the modlog is mostly just there for informative purposes. As in, we can check what mod actions were taken on instance A through the modlog on instance B (and there is no mechanism in Lemmy for other instances to retroactively remove or hide federated modlog items, btw).