Sure, but having music and lyrics that were recorded by other artists in their songs is not derivative, it's plagiarism. Now, it's possible they were just paying homage to who influenced them and maybe they didn't think it was a big deal or that nobody would notice. Perhaps they themselves didn't even realize they were doing it when recording. But multiple times they've been called out for using other people's material.
They're were a great enough band that most fans, myself included let it slide. If it wasn't for Zeppelin most of us wouldn't know about the existence of the songs they took from anyways. It certainly caused some controversy but Zeppelin is still responsible for putting out some of the finest rock albums we will ever hear. The debut is great but I think the five albums that came after blow it away.