The butler/personal assistant is what they call a island host at Rangali. And yes, you are correct that he/she would be the person that walk you to your room during check in, reservation changes, issues with stay.
They will not call you each morning unless there is an issue with your booking (ie: excursion is cancelled due to low particpation, etc). We just came back about two weeks ago for a 7N stay and had two different island host during our stay since the first had to leave for vacation half way throughout our stay.
Our second host was much better, she brought us champagne because our deck umbrella had issues opening and she immediately took care of it and the champagne was certainly a nice gesture. Our initial island host wasn't very great, he just did the minimal I would say. Hope this helps!