I guess I found the answer to my own question in Train Orders.
According to "georgiaroad:"
"The unit was originally a Baldwin roadswitcher DRS type unit. It had its cab removed and became a slug with its trucks changed out with FBs from an old ALCO RS. Later the slug was acquired by a West Virginia coal prep plant. They put a Cummins engine in part of the chopped hood to power one truck and set it up for remote control. They even closed in the right step-well and made it a makeshift "cab."
Not sure why the term bug-slug is used to classify it. This is what Extra2200 South called it when they made mention of its move from Virginia to the Middle Georgia chipper plant. The plant has two parallell spurs pulling off the end of a wye. They use the bug slug to pull the chip cars under the loader. When NS picks up the loaded woodchip cars, they pilot the bug slug onto the leg of the wye opposite the one NS uses to switch it out, thereby getting it out of the way. The whole series of tracks at that operation are on a high fill, so I guess they could not use a trackmobile and due to safety concerns did not want a cable "car-puller." That is pure speculation, but makes sense. I am sure the bug slug was a much cheaper alternative to a brand new trackmobile."
The unit was sighted and photo'ed still operational as of August 2011.
