No, Scion puts a dragon card directly from the library into the graveyard. Grave Pact triggers on things moving from the battlefield to a graveyard.
Note the Oracle text on the card has been updated to say 'Whenever a creature you control dies' instead of 'Whenever a creature you control in put into a graveyard from the battlefield', though they mean the same thing:
700.4. The term dies means “is put into a graveyard from the battlefield.”