Yes, the pirates that spawn in normal space (eg at beacons, RES) won't attack you if they scan you and find only limpets. But the pirates in Supercruise will still babble about you having "tasty cargo" and interdict you or, as LL said, they'll follow your wake if you drop down before they interdict you. Of course, they'll still do all that even if you have nothing at all in the hold and are only "carrying" exploration data or mission tickets, so it isn't really a "limpet problem".