Twitter has serious policies and rules in place to keep manipulation around a subject or a person as minimum as possible. To achieve that they don’t allow automated hashtags. Manually adding hashtags to Tweets is a common practice and can do no harm, while automated ones may be used for manipulation. more here https://blog.twitter.com/developer/en_us/topics/tips/2018/automation-and-the-use-of-multiple-accounts.html
If some hashtags are included in the feed source, that might not be a problem unless it repeats same hashtags in ever post. From a blog-writer stand point, we think they use different hashtags on each post and that’d be ok.
We do support most of the feed specs out there as explained here https://help.circleboom.com/getting-started/rss-feed-sample If any website including Google tools providing a native feed, we can parse and use it.