Multiple USB Storage Devices on Honeycomb
The critical failure seems to be the use of a USB hub.  On my transformer I can mount two different thumb drives and an SD card at the same time.



The left port us USBDrive2, even when only one thumb drive is plugged in.  So it appears to me that it is a honeycomb thing mapping each port to a specific directory, ignoring the possiblity of USB hubs.  Unfortunately I no longer have a USB hub to test this theory on since my wife has watched one too many hoarders shows.

The A500 only has one USB host, but it also has a MicroSD reader in additon.  So an alternative solution you may want to consider is using a micro SD card in your camera in a SD adapter and then popping that into the A500.  A microSD card is quite a bit cheaper than a Transformer + dock.