Here is the response I got from Disney regarding the Drain Voodoo function:
Thank you for contacting Pirates of the Caribbean Online.
The "drain voodoo" skill is intended to drain the power of any voodoo enemy whom you attune and use the skill against. The "drain voodoo" damage will also display in blue above the enemy you are currently defeating. However, due to a known technical issue within the game, this skill is not working as designed.
The Pirates Online Crew is hard at work resolving this error. As soon as the issue is resolved, we will post a notice on the Pirates of the Caribbean website in our Release Notes. You view all the current and past Release Notes at:
http://piratesonline.go.com/v3/#/news/releasenotes.html
We thank you for your patience while we look into this issue and, we hope to see you in the Caribbean again soon!
Fair winds,
Amanda
Pirates of the Caribbean Online Member Services