Of course. But truth be told, I only care about Valve's games when it comes to Steam. But, there are already a great number of games on Steam that already have official Linux clients. Here's a list:
EDIT: List removed. Apparently those were OSX games. My bad. But a lot of games do have Linux clients like id Software games, Epic games, Croteam games, and such.
I think it's reasonable to assume that if Steam
does come to Linux that at least a few game developers would be more willing to make clients for Linux seeing as there are already so many games that support it. Steam would be like the entryway to the Linux gaming world that everyone was afraid to walk through, but with Steam it's a bit more of a safer opportunity.
Of course, maybe not. But at least all those games I listed + Source engine games would be there immediately.
EDIT 2: ChemBro brought up in the TMI forums that there is a linux Steam client already in existence but it doesn't connect to the Steam server yet. Some links:
phoronix.com
Checksums for Steam-Linux-client on Steam-website
Links to Linux-Binaries (they work, somehow)