Not defending dad's previous drug charges AT ALL.
That said, the most recent one was in 2002 - 7 years ago. Even before Haleigh was born. I'm not sure those charges are relevant today, if there aren't any more recent incidents.
And, if dad had custody (which mom fought in a court of law), I'm sure she brought up his past drug history. If I was the judge, first thing I would have done was a random drug test to see if there was concern for any current use.
Dad got custody. That tells me he was at least clean at the time of the test. No further charges, hopefully he got help.