Regardless of what Shimano support says, it does work.
It may not be as snappy as a 10s chain on a 10s chainring, but it shifts acceptably. I am have a bike with an old crankset with 8s unpinned Ultegra 53T chainrings and an old 105 FD that shifts a narrow chain. I agree that the performance is a bit less than what Shimano engineers and sales reps would want for their Dura-ace 10s integrated BB crankset that they sell for $400+ USD, but it works acceptably. I am obviously not shifting up to a 53T chainring uphill, under heavy load at a 40 cadence, so under the usual conditions in which I shift to the large ring, it works fine.
My impression is that Campy and Shimano are both quite conservative in their compatibility recommendations, and maybe for two reasons: (1) fewer consumer complaints if everyone does what they are told and matches up just like Daddy Shimano says to, and (2) sell more product. Following your post, the OP would think that he has to get a new chain and FD to accomodate the crankset, when he really needs neither.
Alot of riders have upgraded to the new integrated BB cranksets (all marketed as 10s) and use them with 9s chains without problems.