You can do exactly that on Friendica, which is another type of Fediverse server. More info at https://friendi.ca and https://fedi.tips/friendica-a-flexible-fediverse-server-type-with-long-posts/
In Friendica, you can follow an RSS feed by just pasting it into the search box and clicking follow. It will appear as posts in your home feed.
You can also follow Mastodon accounts from Friendica, and Mastodon accounts can follow Friendica accounts, because they're both part of the Fediverse.