Couple of thoughts wrt trim specifically.
I doubt there would be a working of the trim in the turns. In my humble aero experience, we generally trim for a fairly high speed, and accept the pull elsewhere. Main reason for this is that the human arm works pretty well at holding and measuring a pull, much less accurately a push. I would imagine this holds for the racers too.
WRT the tab's AOA, it's angle to the free airstream may be increased, but I would question whether it would see much real AOA change - it is hung on the back of a big plate (elevator), which is conditioning a very large part of it's airflow. Further, at those sort of speeds, I doubt there's very much angular movement of the elevator (if you see what I mean). I'm also rather unsure about an increase in 'pull' increasing the roll. You need to increase the roll to maintain level flight/avoid a climb yes, but I don't believe it is causitive. There may be some aerodynamic effect that causes this in theory, however in my experience if I'm hanging out at big bank angles and whale on the stick, it doesn't effect roll one bit.
WRT a trim failure - I suspect the issue is less the overall stick force required for level flight, but the transient. Imagine you're flying along with a slight pull on the stick, and suddenly the trim force is removed. The stick smacks back at you; even assuming perfect conditions, it will take you some time to react and recover equilibrium. This presumably is behind the (much) earlier reported comments from someone saying that they told the race pilots not to use trim. Now assume you've been pulling 4g for a few seconds, and the event suddenly smacks you into the 10+G regime.. Not hard to imagine the world going black before you get it sorted.