There is no manual for this device, so I am unsure where you would've read this.
Nor is HID enabled on this particular device.
And, sadly (for yourself), even if HID *was* enabled on this device, disabling it wouldn't help you at all.
Here's the long and the short of it:
The short - Your Mac is braindead.
The long - Basically, your Mac sees the USB vendor/product ID, recognises an iPod, and then attempts to "talk to it" as if it were running the original firmware, and (as you know), it isn't. This device under Rockbox also has absolutely no idea how to "speak iPod" via the iPod Accessory Protocol. It knows the device is an iPod, but it can't communicate with it in the way it expects to, so this fails.
To make matters worse for you, you don't have the option of mounting the device using Apple's Emergency Disk Mode either (which would work), because we completely wipe out the original firmware and although it is technically possible for us to boot to Apple's Emergency Disk Mode, this fails on this device for an as yet unknown reason.
So...what can you do about it?
That really depends on how committed and/or able you are. You can check out our source repository and compile Rockbox supplying your own USB vendor and product IDs from some form of generic removable storage device (There are some ethical concerns here, though. These IDs aren't free). Where you get those values from is entirely up to you.
The other alternative is using an operating system that doesn't make the same assumptions and simply treats the iPod like removable storage, which (to my knowledge) is everything except Macs, and what you're already doing.
Myself or others here would be happy to point you in the right direction regarding compiling your own Rockbox binary if you choose to go down that path, and finding the USB VID/PID values from an arbitrary removable storage device is trivial.
[Saint]