The effect "Add 1 "Predap" card from your Deck to your hand" cannot be activated in the same Chain Link as the card "Predaplanet".
The effect "You can banish this card from your Graveyard; Fusion Summon 1 Fusion Monster from your Extra Deck, using monsters from your hand or field as Fusion Materials. Only "Predaplant" monsters can be used as Fusion Materials for a Fusion Summon using this effect" activates in the Graveyard and makes a Chain Link. (It does not target. At the time the effect is activated, "Predaplanet" itself is banished from the Graveyard as a cost. Also, it cannot be activated during the Damage Step.)
The application of "using monsters from your hand or field as Fusion Materials" and "Fusion Summon 1 Fusion Monster from your Extra Deck" are not treated as being done at the same time.