In all candor, my opinion is that its more of a fine pocket piece than a workhorse.
Although most of the light appears to be reasonably tight, the weak point is the exposed USB charging port (and the switch) on the ION.
I have an aftermarket USB cover on mine but I would still not subject it to more than light mist. (I would certainly be willing to expose it to more water than I would my cellphone.) With a wrap it might be slightly more water resilient but no it would never be IP rated for water exposure without an external case. Food for thought
FWIW, Surefire a brand known for workhorse lights probably wouldn't fair much better with regard to water resistance with the Sidekick either.