Cedars have been one of the hardest for me to transplant and I'm talking about transplanting 3 foot or less trees with a hand shovel. The success rate was typically lower than other trees although transplanting wild trees is always challenging. I would certainly think you would have better luck choosing smaller trees such that the spade has less chance of cutting roots. Many times, cedars are growing in very rocky ground and those rocks can add to the disruption of the roots as when the spade hits them and disrupts the soil around the roots, not to mention working the spade extra hard. Try to get your trees from softer soils if available.
I did run a tree spade one summer back in the day. I was moving pin oaks, IIRC, and could move about a tree per hour once we got started with a 15 minute drive from plucking to planting. Theses trees were at least 25 foot tall. The empty hole diameter, or root ball/cone, was about 7 or 8 foot in diameter at the top. If you can get the hole and root cone diameter very close in size, it's pretty easy to hand dig the berm around the perimeter of the planted tree (for watering purposes). If the trees sits too low in the hole, you have created a pond and may flood it. If it sits too high, then water will run off the cone and have some difficulty working it's way down around the roots and leave some roots High and dry. I would shoot for size-on-size with cedars with a small berm/mote around it to aid in watering them.
I assume your guy knows this, but we would spade dig the first hole, take the dirt back to where the trees were coming from, drop the dirt near the first tree, pluck the tree, go put it in the hole, dig a new hole, bring that dirt back and put it in the hole where the first tree came from, dig another tree, put it in the second hole, and so on. This leaves one pile of dirt to push in the hole from the first tree.
That's all I know about cedars and spade trucks...hope it helps!
