What trouble? His issue was pot, which is now legal to use in the NFL. He no longer has any issues.
From the perspective of being an NFL player, Gregory's issue wasn't pot. Gregory's issue was that pot was more important than football and the financial security it offered. Think about that. Pot is not physically addictive. The real issue is his mindset and how dependable he could be under that mindset. Maybe he's found enough help to deal with it. Maybe.
The point is, gambling results in a probability of success thus implying a possibility of failure. If a team is going to gamble on a player they draft, they should limit those risks to the 3rd day.
The old Cowboys of the 70's certainly took risks. They drafted a quarterback in the 12th round that had a 6 year military commitment. They drafted a great RB in the fifth round because he had already committed to a different league. They drafted Olympic champion Carl Lewis in the 12th round of the 1984 draft even though he never played college football. They drafted Air Force Academy DT Chad Hennings in the 10th round despite a four year commitment that actually ended up putting him in a war zone.
In the top rounds they took BPA with the highest computer score based on hundreds of attributes. They didn't gamble in the top rounds.