Yes, you can bring up a channel as if its a community by searching it on Lemmy, for example !thelinuxexperiment_channel - then each video will be its own post, and commenting on the post will forward the comment to PeerTube!
If the channel isn’t already “known” by your instance however, you may have to wait until a new video is posted before it is visible to Lemmy.
I added 2 peertube channels to my subscriptions not long after I joined lemmy. So far, they have failed to populate into my feed… I can see the channels in my subscriptions, but when I go to them via lemmy there’s only a couple videos showing and they’re from the timeframe that I added them. However, going to the channel directly, outside of lemmy, I can see that they’ve posted many videos recently.
Odd, it might be an instance level issue potentially. Or rather, an issue between slrpnk and the server that hosts the channel you’re trying to subscribe to.
You can force a video to appear in Lemmy by copying the original peertube URL of the video into lemmy’s search. It will take 2-3 seconds to import it and show up in the search results.
Iirc there was a bug with an older version of Lemmy that turns off propagation of content from outside communities/magazines/channels after 3 days without activity. It might have stayed that way even after the updates. Try unsubbing and resubbing again.