Selected answers from the Dumb SEO Questions Facebook & G+ community.
Justin Y: My opinion: Personally I don't recommend it because the description is for the reader. Adding tags would probably come off as spammy and look unnatural. The description is used to best describe what's on the page and to give the user a reason to click on the results in SERPs.
W.E. Jonk: From the expert panel in this weeks SEO Questions hangout on air on 01:49:41 into the YouTube video: https://dumbseoquestions.com/q/is_it_ok_to_add_hashtags_to_page_descriptions