The question - #hashtags within the text of a post or in the excerpt, what is the SEO effect if any?
Interesting question, and the answer is going to depend on how your audience uses search to find hashtags of interest, and like keywords on the hashtag popularity of usage.
Suggest testing to learn more - as a strategy, consider:
- Use a hashtag, or a couple of hashtags in the title, extract and the body of a post.
- Waiting for your website to be updating into search.
- Search on hashtag(s) to see results.
Very interested in comments about your learnings and findings, also interested when searching if hashtags are treated the same as keywords.