Given that the revoke command is asynchronous, could the cleanup following it (removing logs, xml, dir) be done prematurily while the process is still spitting logs waiting to be killed?

That is a possibility. I haven't explored this much.
If we encounter this, we could think of a way to handle it. Probably need to run another task with a delay to do a cleanup with below checks.

In fact, the succeeded jobs also leave their stuff, so a mechanism to clean that should already be in place anyway. For the typical birds dumping the result in the output directory, there was a cron job for that. Does it apply to Weaver also?

The results that were generated by pywps and cwltool should be all cleaned up following execution by weaver after it moved them to wps-outputs. There should be 3 items {jobId}.log, {jobId}.xml (WPS status), {jobId}/ (output results).

The dismiss cleanup applied here is more specific for OGC Dismiss operation that requests explicitly a cleanup of those outputs, given a user downloaded them.

If the cron job runs inside wps-outputs/ for each birds, then it should pick up weaver as well, but there is not a cron specifically within weaver.