Yeah, no problem in withdrawing cash from ATMs, however there is a ~$400 daily withdrawal limit per account. Another option is to use a foreign credit card at the cage in the Casino Enjoy for cash or chips, then use that for the buy ins.
The Enjoy Casino is not actually in Santiago; it's located about 45 minutes north in the middle of nowhere. There is a decent hotel attached, otherwise I think that the casino has a shuttle to/from Santiago. You may want to check it out with the hotel in advance -
www.enjoy.cl/santiago/en/hotel/
There is also an Enjoy Casino that holds tourneys in the coastal city Viña del Mar, about 90 minutes from Santiago. This is
the schedule with BI listed in Chilean pesos.
Good luck, I'm available for any add'l info you need -