I think this is a standard chromium trioxide oxidation mechanism. The H5IO6 then oxidises the chromium by-products back up to chromium trioxide, making the chromium trioxide catalytic (which is good because it's a nasty reagent so you don't want to be playing with alot of it)
ie.
Cr(VI) + alcohol --> Cr(IV) [by-products] + acid
Cr(IV) + I(VII) --> Cr(VI) + I(V)