I've never noticed any significant FFB lag in iRacing; certainly not enough to cause any kind of confusion. I
have noticed FFB lag in GT6, and even then it's only a problem if I let go of the wheel. There's a study (
link) which demonstrated that humans are generally quicker to respond to tactile stimuli (touch) than visual stimuli, so if anything, humans would react faster to FFB than to visual cues even if there was a small delay.
Interesting. I saw a few comments on their YouTube videos suggesting that they do use FFB, but at a low setting. Maybe it's different for each driver; who knows for sure?
Hurry up iRacing staff, I want to try out the Nurburgring and MP4-30 already!