Usually, yes: IT8 scanner targets are generally made without OBAs, because optical brighteners can introduce fluorescence that would interfere with reliable color calibration.

Your concern is valid. The inks used for the patches are not opaque; they are translucent, so the base material matters. If the paper contained OBAs, its fluorescence could shift the measured patch colors and reduce calibration accuracy.

That said, "no OBA" does not necessarily mean "no fluorescence." At least some targets are made on photographic materials such as Kodak Endura, which may not contain OBAs but can still have a fluorescent substrate. In practice, that can still cause measurable differences depending on whether UV is included or excluded in the measurement.

So the short answer is: IT8 targets are usually designed to avoid OBAs, but the target base can still fluoresce, so fluorescence is still a real consideration in scanner profiling.