Q: Is WP RSS Aggregator compatible with WordPress Multisite?

In a nutshell, yes, the core plugin and all add-ons are compatible with WordPress Multisite.

If you only want to activate the add-ons as network plugins from your main site, then you just need a Single-Site license. On the other hand, if you plan to activate the add-ons and the licenses on more than one subsite/subdomain, then you’ll need more than a single site license.

The latter usually applies when you host multiple client sites in a multisite, which means each one will require a separate license key in order to receive updates and support. If used only on the main site to distribute feed items or posts to the subsites, then a single-site license key is enough.

Please do note that the site license refers to the number of WordPress sites you will activate this license on. It does not refer to the number of feed sources you can import from. In fact, the number of feed sources per site is unlimited.