Can two Powered Up train motors be plugged into one hub I have set #60198 and it comes with one Powered Up motor. I'm hauling many many cars and one motor isn't enough any more. I see there is a slot for "B" on the hub. Is it possible to plug in another train motor into B and have the train be powered by 2 motors? 

Does it even help? Not sure if a second motor would just split the power between the two motors if it worked, or does it draw 2x the battery from the hub?
You can attach second train motor to B output. However it will be controlled independently from motor attached to output A. So you would need to control speed for each motor separately.

Speaking of traction. The key thing here is your train weight. You might consider putting another full battery box (unpowered) into train just to increase weight and get more friction between wheels and the track.