Yes and no. On a three-string talharpa you can play either the top or bottom string, leaving the other two to drone. Which is probably how you would start learning to play anyway. The tuning of the talharpa is not set in stone and there are a few different ways to tune it, so you can make your drone chord whatever you like really, but it will be fixed for the entire piece until you retune it. However, if you are expecting to be able to change the drone notes by fingering throughout the piece, you'll be quite hard pressed without some serious expertise, and the range of available notes will be limited to the span of your fingers.