No, no sense in it. Fiberglass's benefits are realized in its resistance to compression and tension forces which are exerted on the back and belly surfaces. The core is considerably more nuetral and if anything, would benefit from something lighter, to take up space, such as light weight wood, foam, even carbon would be better than fiberglass. If a bows wooden back and belly can handle those compression and tension forces.... like hickory and osage can, there's no need for glass anywhere, it just slows a bow down. As such, the core would be the worst place you could put it.