I looked up their site to see if they had any photos of previous events, to see what people were wearing. No luck. So I just went to Google Images and searched for Whisky Live. Got lots of photos. It looks like people dress from very casual (untucked shirts and shorts) up to suits and ties. So it appears to be an "anything goes" type event, in terms of dress.

That said, I'd still dress up a little. I'd wear a tie.