Castile soap is made from Olive Oil. Though it is great for the babies tender skin, it can coat the cloth fibers and the wipes. This may cause the diaper insides to be sticky and may attract dust. Eventually the wipes will be less absorbent too. It may also cause repelling over time.
In general a small amount may be fine of course. It could be an issue down the line. But if the amount is minuscule it should be fine, but we recommend skipping it if possible!