There are various options for plates. The typical is titanium mesh which is then covered with an acrylic or ceramic material. There are also fiberglass molds which can be used, but require pre-surgical specialized imaging and ordering of the mold. I am not familar with this dermatologic condition, and could not find specific references to it in the literature with regard to cranial plates. The arteficial plates can cause a local reaction, but in most people this is limited. Another possibility is that your husband had a reaction to the suture material used. This can be tested by seeing an allergist.
With a more formal consultation more definiative information could be provided. Perhaps a second opinion with another neurosurgeon at an academic center would be reasonable. Good luck.