Maybe is it a feature that is not build on newer or older VT30?
Or maybe does it only work on the VT100, even if some people said it works on their VT30 (they may be confused about effects).
But let's try some things.
Before doing what is following, I would set the amp on manual mode, and then, even if the selection knob is already on "Pitch", I would turn it a bit then reset it on "Pitch".
1/ First, did you check the mix ?
(I would try with a clean sound, then set the selector on pitch, verfying I'm hearing the two sounds - if not, I would turn the mix Edit1 button until I hear both at the same time)
2/ Then, is the Tap knob changing the pitch? (at the amp panel)
(If the answer is "Yes", I would retry with the ch2 now)
On the video, they did insert some sequence, showing the selector being set to the pitch effect - I did notice the amp was on "Preset" mode, not on "Manual" mode - but as Dave Martone is later speaking about manual mode, maybe these pictures are just post-production mistakes. (the ch2 would change preset in this configuration, I think - but would have a try to be sure of that)
3/ Finaly, when you set the selection knob to the delay effect, is the ch2 switch changing the delay time? (You said it's ok above, but to be sure ...)
Try that and if it 's ok just change the selector to pitch shift, and retry.
The fact that you did some trials on VT50 and VT30 in a music shop would indicate:
- the footswitches had a problem
- all the amp you tried with had a problem
- the feature is not set on these amps (may be set on VT100 or not - features can be modified without notification, as always)
- you do some bad operation
if you can go to other music shops, let's have a try with their amps and their footswitches.
Maybe could some Vox people tell us if this feature should work or not with your amp ...?