The word "hobbit" existed as a Welsh term of measure (four pecks of grain, each peck weighing forty-two pounds), but I can't imagine we wouldn't have heard if it had existed as the name of any sort of mythological personage before Tolkien.

("hobbit" is also found multiple times on Google Books as a scan-o for "bobbit", "babbit","hobbie", "habebit", etc., by the way)