If there are 3 copies of Keeper of the Shrine in the graveyard and a dragon is destroyed, can you summon all three back and get 3 dragons if normal? Or can you only use one a turn?
CDClarke is correct in his answer; you cannot do that what you propose.
To enhance on the reason why it is once again important to note that specific part:
You can only use this effect of "Keeper of the Shrine" once per turn.
One thing that this specifies is that only this effect has restrictions; you can use the "This card can be treated as 2 Tributes for..." part as many times as you want/can.
Another relevant thing to notice is that this quote references to the card in general. This means that the restriction applies to any Keeper of the Shrine you have.
You could do what you propose if the card text said instead "You can only use this effect of this card once per turn." Card texts that you see contain such phrasing or similar refer to that specific copy of your card, restricting it from being repeatedly used (however it does not restrict other copies).
It is important to note those two different situations to effectively tell apart from a restriction that applies to a copy from that that applies to the card in general.
Let's read through the text box of Keeper of the Shrine.
This card can be treated as 2 Tributes for the Tribute Summon of a Dragon-Type monster. While this card is in your hand or Graveyard, if a face-up Dragon-Type monster on the field, except "Keeper of the Shrine", is sent to the Graveyard by a card effect or because it was destroyed by battle: You can Special Summon this card, then, if that monster sent to the Graveyard is a Normal Monster, you can add 1 Dragon-Type Normal Monster from your Graveyard to your hand. You can only use this effect of "Keeper of the Shrine" once per turn.
Pay extra attention to the part I've emphasised at the end. The wording of this clause is known as a 'hard' once per turn, because it specifically restricts you from using the effect of any card with the original name 'Keeper of the Shrine' more than once in a turn. So, unfortunately, you'll only be able to get back one Keeper when a dragon is sent to the graveyard, even though they're separate cards.