As saratoga stated, this should "Just Work".
At this point (with Rockbox installed), the device (the iPod) is essentially just generic removable storage, which modern Android devices with USB-OTG can make use of quite readily.
If it works with standard generic USB flash media, but doesn't work with the iPod, one possible explanation is that it is recognising the USB VID/PID (vendor and product IDs) to recognise the hardware as an iPod and attempting to treat it as such, and then it freaks out when it can't find literally any of the expected database structure or even a single solitary shred of the original firmware.
For any of the other Rockbox-supported iPod devices this is not an issue, because we leave the original firmware largely intact by default, as well as the device's file system and directory and database structures, and we don't remove the firmware partition. On the iPod 6/7G, none of those things are true - it is somewhat of a special creature in this regard.
Fortunately, we do not need to speculate about whether or not this is the issue. With the magic of science, we can test this issue, by way of telling the host (the Android head unit) that the device is in fact not an iPod. In this binary
*, a patch
has been applied to the source prior to compilation that changes the defined USB VID/PID to unassigned values.
The take-away from all that jargon is that with that binary installed the device will deliberately misrepresent itself, and if all goes to plan, the Android head unit should then be happy to treat the iPod as a generic removable storage volume.
If this is the case we then know that the head unit is attempting to be "smart" and treat the iPod as an iPod, instead of a generic storage volume.
If this is not the case and installing the linked binary does not have any effect, then I suspect you would want to talk to the OEM (Original Equipment Manufacturer), and not Google (whom I believe you were referring to when you stated 'I haven't asked Android'). Google's oversight of the Android operating system is probably not as tight nor as ruthless as one might imagine, it is quite likely that Google is entirely unaware that this hardware even exists.
If the issue does rest with the head unit, and it cannot be solved by tricking it into thinking that it isn't dealing with an iPod, it is incredibly unlikely to ever be fixed. Many OEMs are incredibly unwilling to push any updates that do not fix either exploits or critical vulnerabilities, even for widely supported and adopted devices with always-on style mobile radios, let alone car audio systems. This has multiple facets, but the obvious ones are:
1 - Any time and effort spent fixing, updating, or upgrading the previous platform is time that isn't spent working on the next iteration of the platform.
2 - If you have ready access to operating system updates you are far less likely to upgrade the hardware in order to receive the latest operating system updates.
*This binary is generated by a third party, and like the official Rockbox binaries, comes with absolutely no warranty or guarantee of functionality - either express or implied. This binary is modified, but only for the sole purpose of reporting fake USB vendor and product IDs for the sake of testing and/or complying with overzealous hardware and/or software.