I have talked to the bartenders in great length and the have told me that US dollars are fine and worth more. We all know that they bust ass so we tip very well.
I always tip in USD and I always meet or exceed standard American tipping etiquette. I also buy and bring a big box of chocolate candy bars from Costco and tip the young men with those.
We always bring tip money. Funny to see when they reconize you year after year. Kevin says because alot of guest dont tip...which is sad. They work their butt off for all of us!!
Only my opinion, but I think it's nice to tip. Breaky, dinner, my room, bartenders and if a drink is delivered to me. Just the way I was raised.