I looks like the Canon menu allows: 100, 200, 400, 800, 1600, 3200, 6400, 12800
The ML menu lets you choose from: 100, 160, 200, 320, 400, 640, 800, 1250, 1600, 2500, 3200, 5000, 6400, 12800
1/3 stop ISO increments would be: 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250, 1600, 2500, 3200, 4000, 5000, 6400, 8000, 10000, 12800
So short answer, no but close enough. Longer answer:
You can go into the Canon menu, 4th wrench, Custom Functions(C.Fn) I:Exposure and choose between 1/3-stop and 1/2-stop increments. This will allow you to set the shutter speed and F-stop to 1/3 or 1/2 stop increments. So you can still expose to 1/3-stop accuracy if that's what you really want.
By the way, my understanding is that some of the ISO settings are interpolated, gain up or gain down, from the actual ISO and can introduce noise. In addition, when shooting raw it is best to expose as far to the right of the histogram as possible without clipping in order to record with the highest signal to noise ratio and when doing this quite often a higher ISO will exhibit less noise than a lower ISO. To make matters even more confusing the very high end cameras like the RED and Arri Alexa perform best at their "native" ISO and cinematographers go to great lengths to make sure they shoot at the optimum ISO as well as the best f-stop for lens performance and depth of field and they are pretty much limited to the shutter speed they can use so they have to make the best of it with their lighting and use of ND filters to nail their exposure--then they spend countless hours in the color grading suite getting exactly what they want.
