Sarah,
I'm thinking of using this for one of my groups to let a podcast I
run post as long as i have special tags in said podcast.
Interesting.
But I don't know of a way to set things up so that podcast postings lacking certain tags would be automatically ignored. Unless you can do it with something like IFTTT.
Question two. Would list members still be able to reply to the
message on the list, ...
Yes, provided that the group is set to have replies sent to the group. I'm not sure what would happen if Reply To was set to "Sender". Also assuming you didn't use a Hashtag to restrict or moderate replies by members.
Shal
Shal Farley