Answer:
Success is viewed differently with different perspectives.
In the case of the unfortunate colonists, since their fate is unknown, this question cannot be answered for them.
However, for the English empire, Roanoke was a stiffening blow to their move to colonize the new world of the Americas, and it was until 20 years later that the Jamestown colony was established.
For the Native Americans, the disappearance of the Roanoke colony meant 20 years free from European imperialists, which would make the colony a success.
Then, for the aliens that successfully captured and probed the Roanoke colonists, I'd deem the colony to be a success, as they were able to complete their mission without compromising their existence to the humans, and they were able to gain critical information about the human race, setting them up for December 21st, 2012, or the end of the world.