What reasonable steps can I take to report misbehavior by publishers to the wider research community? What resources are available for reporting unethical practices or misbehavior by publishers? I'm aware of Beall's list, are there other efforts to objectively identify publishers with low standards or other practices that are detrimental to the research community?

Is it helpful to submit info to organizations like COPE?

This meta discussion is of interest and might suggest that AcademiaSE is not a suitable venue for sharing information on specific practices.
If the matter concerns a mathematical journal, you can submit your case to the European Mathematical Society ethics committee

Note that even if this committee has been established by the EMS, they should consider non-European issues as well as issues from European publisher, journals and authors.

Of course, their power is somewhat limited but given their status, they could have some impact by simply issuing a public statement.