The piwik.js should be fixed to allow campaign tracking within the hash tag parameter.
I have updated FAQs to reflect this new feature:
Also updated the "Tracking Campaigns analytics" doc.
The disadvantage to use Hash tags for campaign tracking, is that it breaks the hash tag, which some websites or app require. If your site/app uses the #hashtag, do not use this technique. If you don't use the hash tags, then consider using this technique, as i believe it is slightly superior (as it does not create duplicate URLs in search engines index).
In 15277fb: Fixes #3953 now detecting campaign parameters within the hash tag as well