There's two kinds of latency at play here, no?
The first one, let's call it "control latency", is the lag between the player's manipulation of the physical whammy bar and whatever the floor unit needs to do in response. I imagine this should be very close to zero, as it only requires a relatively "lean" control signal to be transferred and processed. Wiggle the bar and the floor unit should react virtually instantaneously, even if the connection were wireless, as there's no audio stream passing between the whammy bar and the floor unit.
The second kind of latency, let's call it "audio pitch shifting latency", happens entirely within the floor unit and is inherent to any pitch shifting algorithm. You would theoretically notice it when picking notes while holding the whammy bar down, for example (like chu says, not something you would traditionally do a lot), or using the "virtual capo" feature.
It's entirely possible this device has less pitch shifting latency than the Kemper, although I personally think the Kemper's is not bad at all. However, "zero lag" seems like marketing hyperbole when it comes to this kind of latency: real-time pitch shifting simply takes a non-zero amount of processing time. Like Monkey_Man said, the best you can hope for is "not-perceptible" (which is good enough, of course!).
That said, I would be interested in this without the on-board audio processing in the floor unit, just as a (preferably wireless) control device. Make the floor unit simply output a MIDI cc or expression pedal voltage signal and leave the processing to the Kemper!
The only challenge would then be that the Kemper expects a traditional expression pedal, which is unipolar, i.e.: it goes from zero in the heel position to 100 in the toe position. To use this as a whammy bar, which goes both up and down, you'd have to be able to define a middle position in the Kemper where the guitar signal is unaffected, which could take a bit of tweaking to make it correspond to the whammy bar's physical middle position. But it would be cool to use it for morphing!
Edit: I guess the latter issue could be solved if the floor unit acted like two separate expression pedals, one for pressing the bar down and one for pulling it up. Connect it to the Kemper using two TRS cables and you can control two different effects, depending on the direction!