Searched exactly that question!
Yes, there should always be at least this one hashtag:
By that we may raise the probability to get spoiled into the timelines of those people this whole site is relevant for. Without the
#Drupal hashtag these tweets most likely will just run through without anybody noticing them. As
#Drupal already is a widely accepted hashtag, we should go for it.
Look at the screenshot below. This tweet got tagged
#blocks. But who on Twitter to reach with that tag? It's an in-site relevant tag. But outside of Drupal Answers this tag does have zero relevance. If it at least would have been
#react that would be different. All tweets from here really must use
#Drupal as this is what this tweet in a broader context is about. Upvote if you agree.