One of those silly things that is on paper somewhere but nobody pays any attention to it. And that includes the government. Early on when ACUs first came out the military made a lot of noise about this, obligating the commercial manufacturers to not put the IR tabs on. So what happened? You had to order the IR tabs separately and put them on yourself. This was advertised right out in the open since there is nothing illegal about that because the IR materials are commercially available and the US military has no authority to regulate their sale or use.
In theory pretty much all cloth items are "controlled", IR tabs or not. All cloth based items are supposed to be destroyed or otherwise rendered unserviceable before being released from the military's control. The problem with this is nobody provides the military with the money to destroy the items and yet also tells them they should earn as much from surplus as possible.
Talk about conflicting signals
In short, I wouldn't worry at all about it. If the bad guys out there want something they don't have to get it from the US... they can order it from China. Nobody in a real life situation would ever notice the difference.