Most of the RSS feeds are fully open to anyone. However, there is also the possibility of offering a closed or payed RSS feed only to subscribers.
Advertising in RSS Feeds
Monetizing RSS feeds is viable. Many advertisement companies offer the possibility of inserting advertisements in feeds. The ads served must be related to the RSS feed content. When the volume content served is important, advertising in RSS feeds will be a success.
Google AdSense for Feeds used to offer contextually targeted text and image ads. However, the service was discontinued by Google.