I would hate to see a stand up with a carpet pole with the mast about 7 feet in the air make a sharp turn!!! Carpet poles are safer on sitdowns.

I would not recommend replacing a sit down with a stand up in their application. Stand ups have their special places but I would think this is not one. I had a customer (in Texas) with a Dockstocker that I did some training for. They had taken a tow strap and wrapped it around the back of the unit so as to "help" keep the operator in place. They had a small location and travelled in and out of a (OMG...wait for it...) concrete culvert.
Scary stuff, guys be careful whichever way they go........

They must be handling fairly small rolls if they are using a 3000 lbs. forklift. A couple of warehouse distributors that I service all use 5000-6000 lbs. lifts to handle rolls that are up to 3' in diameter. I've seen very small retailers use a 3000 lbs. lift but they won't pick up a large roll.

You are best advised to get the rating from the manufacturer or their local dealership - too many variable for you to "Guesstimate" and too much liability for you & your company. You will need to be armed with the weight of the battery installed in the unit, Weight of the rug ram, lost load thickness of the attachment (dimension from the front of the carriage to the point that contacts the carpet roll), pole length, max. length & weight of the rolls to be handled, what mast & lift height is on the unit.
G.L.