The Devils Media Guide lists the record for most goals in a season by a rookie as:
21 - Kevin Todd (1991-1992)
21 - Jeff Larmer (1982-1983)
20 - Pat Verbeek (1983-1984)
Franchise Record
30 - Paul Gardner (1976-1977)
I can't believe I forgot about Larmer, but at least I got Todd correct.
As for Semak, he was born in 1966, meaning he was probably too old to be classified as a rookie in 1993 (the "Makarov rule").