Hi,
Yes, the depth control lever can be on when the drawbar is, it has to be on at the same time to use a plow.
The drawbar can be in either the rear position or the front position.
The lever mounts on the 2 holes above where the drawbar goes.
You might want to remove the vertical part that attaches on the drawbar, so it isn't hanging down to catch on things.
Below is a pic from TM Tractor showing the lever in position. The drawbar is in the front position in the pic, and it has a Cub 193 Plow on it.