If you Tribute a Hieratic monster as a cost, You can still Special Summon a Dragon-TypeNormal Monster. The Special Summon effects read as follows. “When this card is Tributed: Special Summon 1 Dragon-Type Normal Monster from your hand, Deck, or Graveyard, and make its ATK and DEF 0.” Hieratic Dragon of Gebeb must Summon a “Hieratic” Normal Monster, but the effect is the same other than that. This is a mandatory effect, so it’s going to activate no matter when or how your Dragon is Tributed.
The Special Summon effect does not Chain to whatever Tributes the Hieratic monster. This Special Summon effect is a Trigger Effect. Trigger Effects are Spell Speed 1, so they don’t Chain to any already activated effects. They have to wait until any current Chain is finished, and then all Trigger Effects that were triggered in the process will begin a new Chain afterwards.