SNIP, the Structured Data Plugin for WordPress allows you to create Rich Snippets that produce stars in search results. However it does not allow your users to rate your blog post as it’s not a rating plugin. That means it has no built-in rating system that counts automatically.

However you can add a rating (from yourself) into structured data snippets. This is especially interesting for bloggers who write reviews and rate the product they have reviewed.

If you want to connect a third party rating system into a Global Snippet, you can:

• check if the ratings get stored into WordPress’ post-meta table. If yes, you can use the “Post meta” field type for a schema-property. Check out this FAQ page for more information on how to do this.
• If you don’t know where the data of the third party rating plugin is stored, ask the developers!
• If you work with a plugin that is publicly available (not a purchased one) you can also ask me. I can have a look as well an can maybe guide you to the right direction.

As always: check out the documentation page for updated information about this