as with many things with a foreign country, what you are told is not always the case LOL
The hotel prefers you to book thru them bc they make money on it, and chukka may well make more money if you book thru the hotel, but its not nessesary. It is convinent though
However when i was there 4 years ago, and 3 weeks ago we did not book thru the hotel and still did the chukka's river rafting and thier appleton river tour.