No, sechsgang, that's not true. The wheel offset ultimately determines whether the wheel moves in or out from the vehicle, regardless of the wheel width or backspacing. In other words, a 7-inch wide rim with 0mm offset and an 8-inch wide rim with 0mm offset will both "stick out" the same distance because the wheel mounting pad/surface is directly in the vertical center of the wheel. The backspacing of those two rims are different, of course, at 4.0 inches and 4.5 inches, respectively... but that makes no difference.
In jscheu's case, he would be going from a rim with +30mm offset to 0mm offset, which is a 30mm change. Since 1 inch = 25.4mm, his stance would be 1.18 inches wider on each side of the truck (2.36 inches overall). IMO, that would look great on a lifted truck with wider tires. But on stock height and skinny tires, it would look a bit odd.