I looked at the GSW website and read part of the installation instructions of a direct vent WH. It says it can be installed on a carpet, if you install it on a panel. I'd think that it might be prudent to put a drain pan underneath, and then you could run the laminate underneath (course, you'd have to drain and lift the thing first). I don't think you'd have a problem running the laminate right up to it. Best to just confirm with their tech support line for homeowners 1-888-GSW-TECH (479-8324). It's free, and then you'd know for sure. Since the heat rises, and the flue can get quite hot, it's important to have clearance aboveand to the sides for maintenance. Not so much beneath.
The biggest thing for the base is to ensure it is stable as you'd not want to have the thing tip. And, because most laminate doesn't like water at all, a pan underneath is a good idea. If you don't run the outlet to a real drain, it still has some advantages, since often (but by no means always), a leak starts out slow and small. If you notice water in the pan, you can fix it before it become an issue. It can progress from small to huge in a short time, but usually, you've got some time to react.