Hm. I haven't looked into WordPress’ AP implementation yet, so I don't know if FediFetcher can support it. But generically what I would say is that FediFetcher does the following:
Using a combination of the .well-known/nodeinfo and .well-known/host-meta endpoints it determines the host software (https://github.com/nanos/FediFetcher/blob/95b644d4319a8755684f5347ef47ce6b2a38cae1/find_posts.py#L1101)
It then uses that info to determine if the host supports the mastodon, misskey, or lemmy API (https://github.com/nanos/FediFetcher/blob/95b644d4319a8755684f5347ef47ce6b2a38cae1/find_posts.py#L1205)
If the server identifies as supporting any of these APIs, FediFetcher fetches comments using the detected API. Otherwise it will not try to fetch comments, because it only supports these three APIs.
So, from my POV the questions are:
1) Does the WordPress AP integration support any of these 3 APIs?
2) Does the WordPress AP integration use either the nodeinfo or host-meta endpoint to identify itself?
If the answer to both of these is ‘yes’, FediFetcher can easily support the WordPress AP integration. Otherwise it gets more complicated.