Scion of the Ur-Dragon and Grave Pact
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.”