Well does the property owner know why it went on top of a stump? Was it to replace one in a line so it had to be there to match others? Someone has to know and someone had to have a reason for it. maybe the owner didn't want to pay to have the old stump and roots completely removed so they accepted the alternative. Again, what would you have done?
No one is going to say it's proper, but again when you HAVE to do it-- well, throw in an extra dead fish and two pennies and hope for the best.
Guarantee it?
Yes-- for twice the normal price. If the h.o. insisted on the exact location or if the design required it, I would do it and say "if you want a guarantee I have to charge you more due the increased chance of it not doing well." If the property owner wants to share the risk, normal price no guarantee.
A wild sapling on a stump vs. a healthy nursery stock with a temporary hampering of a broken root ball and a human caretaker??? I'll bet on the tree with a homeowner, some TLC, and fertilizer.
How about a bareroot planting?
I had a neighor who bought (REAL cheap) some birch from a 'grower' to find the roots had not taken to the soil at ALL. He pulled the tree out and the soil literally fell apart and the roots were pretty much buc naked! Apparently grower had just transplanted into containers as bare root. Neighor planted them (4) anyway and 5 years later they are doing fine. He asked me what I thought the chances were of them surviving-- wish I knew the term "Slim Shady" back then.
To that point, IF I had to, I would take a b&b and let all the soil fall off (gently) and then plant it on top of a stump IF necessary. I've seen worse!-- like scapers leaving wire around trunks. The drawing says 'container' though if size matters to anyone. Either case, it's pretty much the same I would say.
Here's a funny pic I call "get bent". Well I think it's funny to look at.