Yes, I know I'm lucky . I can't imagine to stay in another hotel in Siem Reap
For the tuk-tuk, I always use the same every year. The 1st time I used his services, he was just one of the tuk-tuk waiting in front of the hotel (so the answer to your question is yes for both points as he's working preferentially for the Sofitel). The following year, by pure chance, he was there also at the time I was needing one. And since that, I make sure when I arrive to advise the doorman of the Sofitel to look for him and to tell him to be there at a certain time. It's nice to have established a good relationship with him because he's a nice guy and of course because I trust him. I have his card with phone number & e-mail address if somebody's interested.