SAS are unlikely just for reasons of geography - they are based on the other side of the country.
But there are two Commando Regiments, and a Navy Clearance Diving Team, all with people in Sydney - all trained in the type of skills needed in a situation like this one.
Police to soon give an update on hostage situation here live:
http://globalnews.ca/news/1726280/hostages-being-held-at-cafe-in-sydney-australia/
Whoever they are I don’t doubt they’re as good as it gets.