Well, this made for a fun morning. The Siemens 1500 PLC kept not seeing the KRC4, even though we had all the configurations matched up.
The one odd thing was that this system's integrator was using Profinet Device Names that start with numbers, rather than with letters, a situation I've never seen before.
What we eventually figured out was that, when the PLC programmer entered the Device Name for the robot, the Siemens software popped out a "Converted Name" that looked like the software had taken the original alphanumeric name and added some decimal-based ASCII codings. Once we tried copying that into the Device Name field in WorkVisual, suddenly everything worked.
Apparently, the older Siemens PLCs would not allow you to create Profinet Device Names that start with a number, but the 1500 series will. But this violates that IEC naming convention, so the Siemens software automagically generates a "Converted Name" that does comply with IEC conventions. Since the vast majority of Profinet devices being connected to a Siemens PLC will have their names automatically, remotely assigned by the PLC (and/or TIA Portal), I suppose that works for most situations. But the KRC4 needs the Device Name to be set manually in WorkVisual.
One additional item of potential confusion: we were also using some capitalized letters in the Device Name in WorkVisual (5.0), and WorkVisual popped out (just below the Device Name field) a "Converted Name" of its own, but this "Converted Name" did not match the Siemens "Converted Name" -- it only converted the uppercase letters to lowercase. So it appeares that WorkVisual and TIA Portal use the phrase "Converted Name" to mean different things.
So, something to be aware of for the future. I don't have any time to try different ProfiNet versions or older WorkVisual versions, so I don't know if this whole mess is related to the specific versions being used on this project, or if it's a more general thing. But from what I'm being told, the older Siemens PLCs that prohibited DNs that start with numbers are being phased out of the market, so we're liable to run into this situation more often as time goes on.