Yes, if there's actual IR present. Even when subtle (and depending on the camera/lens/sensor), the changed blacks are the first thing I notice when IR is present, as they usually tend to go a brownish/reddish color on camera.
But it also depends on the material doing the reflecting. I once shot a promo with a four person Mariachi band all wearing tuxedos. All the tuxes looked black to the naked eye, but depending on the material used, they went different colors on camera from subtle browns to subtle greens. The only one that remained black was the one that seemed to be made with cotton. 100% cotton seems to absorb the IR and not reflect it back into the lens.
It has been my experience that a well used all cotton flag shoved in front of the camera can often be used as a 'standard', since unless the IR is wildly out of control (shooting outside in bright sunlight with a ton of non-IR coated NDs), it will remain black in the presence of moderate IR. I used to use that trick to answer the question of "Why are the blacks different colors? What's wrong with your camera?" If the flag stayed black, the answer was "Nothing at all."
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