'You can only repair disk permissions your root drive (ie the one running OsX).' - is an incorrect statement.
The current boot volume will only enable 'Disk Utility's 'First Aid' tab panel's 'Verify Disk Permissions', 'Repair Disk Permissions', and 'Verify Disk' buttons.
Any volume (other than the current boot volume) with a valid (bootable) MacOS X 'System' folder, will enable 'Disk Utility's 'First Aid' tab panel's 'Verify Disk Permissions', 'Repair Disk Permissions', 'Verify Disk', and 'Repair Disk' buttons; otherwise, only the 'Verify Disk' and 'Repair Disk' buttons will be enabled.
If a volume is partitioned - selecting the volume (within 'Disk Utility's 'First Aid tab's panel) itself will only enable the 'Verify Disk', and 'Repair Disk' buttons. Selecting an individual partition will enable the 'Verify Disk Permissions', 'Repair Disk Permissions', 'Verify Disk', and 'Repair Disk' buttons - if a valid (bootable) MacOS X 'System' folder exists; otherwise, only the 'Verify Disk' and 'Repair Disk' buttons will be enabled.
The above information is based on using MacOS X 10.4.4.
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Whether or not a volume is recognized, is not determined by 'Disk Permissions'.
Stating Kanguru drive is insufficient, considering the number of models produced - aSATA and USB, USB only, FireWire only, and also USB and FireWire.