The way the Incra Ultra Fence works is quite different than the regular SS fence.
The fence actually rides in a carriage that is attached to a floating table. Each time you place the Incra fence on the SS you can (and should) zero out the fence by bringing the fence up against the blade. You can then do a rough zero alignment, and then (this is where the Incra fence really shines) you use the micro adjuster to bring in the fence to the blade until it is just touching an outside tooth on the blade. You then lock the fence down and then move the ruler(s), that are held to the incra carriage with a magnet strip, to zero (or another measurement on the ruler you prefer) under the cursor.
Of course you will want your SS saw table and miter slots to be aligned with the blade for any type of cuts you are making using any kind of fence or miter gauge. But with the Incra fence, you can actually fudge on that a little. Because the Incra fence is attached to a floating table, you can also adjust the alignment somewhat by loosening the connector tubes (the fence comes with the 5-foot connector tubes and those are the ones recommended to use) and tapping the floating table until the blade is contacting both the infeed and outfeed sides of the blade. You then lock down the floating table and use the fence's adjustment system to do the final calibration. You can get away with this because the the Incra fence actually floats on the table's rails and does not clamp down onto the saw table.
I actually tested the accuracy of the fence with digital calipers. I zeroed out the Inra fence rulers as I wrote above. I used my dail set-up gauge to check the flatness of my blade to make sure it was attached and aligned to my SS as well as it could be. I then moved my Inra fence back the width of the wood (6 inches), and then moved the fence forward 3/32" (kerf of the blade) and using the micro adjuster moved it forward another 001."
I was able to rip, or shave, a less-than-paper-thin piece off of my test piece, and I was able to do this over-and-over by using the micro adjuster.
I measured the test pieces using digital calipers and each piece came out nearly perfect. What I mean by nearly perfect is that no saw blade is perfectly flat, and this is what was reflected in the test cuts. All-in-all, the test pieces measured more than above average as being .001" thick.
So yes, it is possible to rip cut wood .001" thick, though I see no point in needing stock this thin. What it is great for is making precise cuts for you projects. And if you need to shave off just that little bit to make a piece fit, or several pieces fit, you can't beat this Incra system.
And did you know you can also shave off .001" during crosscuts using the Incra Miter 2000 and Mitersled 5000. Using the Incra Shop Stop that attaches to both of these systems, you can move the stop forward and back using the micro-screw and the rulers attached to these fences as a guide. I've tested these systems too and are as dead-on accurate as the Incra fence.
Of course, the saw table needs to be in alignment. But it should be for any type of accurate cuts anyway.