Is there any license issues using the maps made in Hammer in your own projects btw?
In theory you can only use Hammer for HL mods or free games. For use in a commercial product, you must pay a license. I don't know if they will continue charging money after the release of HL2 (there will be a new version of Hammer, maybe they make the HL1 version available for whatever you want, who knows).
They won't know which map editor you used, but I don't recommend trying to fool them. I prefer to use Qoole, which is very good, easy and free.