Check out !worldnews@lemmit.online. The admin of lemmit.online has set up a bot that fetches reddit posts via RSS, making it much easier to make the switch and of course not getting any ads.
You can make requests for subs to fetch at !requests@lemmit.online.
In the end we’re just using lemmy and lemmit’s bot as a simple RSS reader, so nothing illegal or even remotely unethical happening here.
If you visit Lemmit.world, you can post requests and they will go into a community in Lemmit.world. It’s been set up as a sort of Reddit mirror, and people can subscribe to those communities from across the rest of the Thrediverse.
I think if you wanted to pipe into an existing community then you’d probably be looking at running a Bot yourself that can post the content directly into that community in the same way. It may be worth asking on Lemmit.world to see what is involved, but also on lemmy.ml to see if that is an acceptable thing to be trying on that instance.