Photo Credit: Jewish Press
According to the opinions disallowing the gid hanasheh to be used, we need to explain how the blood of the eilim was used in the Mishkan, since there was never a time when it was permitted to be consumed. The Noda B’Yehudah (Tenina Orach Chaim 3) explains that only something used for coloration purposes was allowed to be from a forbidden material. Therefore the blood of the eilim was permitted to be used as a dye.
Similarly, we can suggest that those who hold that the cheilazon was a non-kosher worm allowed it to be used in the Mishkan because it was only used for coloration purposes.