Andrew Bliss is the Valve employee who was just slotted into the UDS-R schedule to speak on Monday afternoon in Copenhagen. The talk can be found here, but there's no details beyond stating "Drew Bliss - Valve."
Drew Bliss has only been working at Valve since March of this year. His LinkedIn profile states he is a developer working on Steam web and mobile support. When I was out at Valve in April, Bliss wasn't part of the "Linux cabal" and I'm not aware if he's since joined the Linux development crew or is working outside their group.
We will have to wait until next week to find out more details of the Valve Linux talk at UDS, but it will likely be about their Steam Linux beta for Ubuntu. At least the Valve Linux talk will be more interesting than the worthless Electronic Arts talk at the last Ubuntu Developer Summit.
Ubuntu is the first Linux distribution that Valve will be officially supporting. Canonical is now working hard to make Ubuntu a great gaming platform due to major opportunities presented by Valve supporting Linux, Gabe becoming more open-source friendly, and it would be huge for Canonical if Ubuntu Core ends up being the chosen Linux platform for powering the "Steam Box" console.