I was out with a bunch of work mates from a start-up software company one evening, and we were going to go to the American Bar for a cocktail. I was a client services person at the time, so was wearing a jeans, a button collared shirt, and leather shoes. They stopped us though, as many of the devs were in t-shirts, jeans and trainers (sneakers). The thing they pointed to was the shoes. T-shirts seemed acceptable to them, but trainers were not.

This was in 2010/2011, so things may have loosened up by now. But might be worth checking with the hotel exactly what they think smart casual is.