Yes, the Steam key is different. You need to get it by registering your CD key at the Slitherine site. It's easy to get, you just have to follow the few clearly enunciated steps.
The steps are not clear... and the word "enunciation" implys a certain level of exactness, which is lacking.
Whether you use the ULS first or have to have a Slitherine account first is unclear. As it turned out I never actually had to register on Slitherine to get into the ULS, but I only discovered this by stumbling around. (After looking at the ULS, it appears that I was given a Slitherine account by virtue of having purchased Civil War 2 from Matrix, but I have no idea what my ID or password would be because I wasn't the one who set it up.) When you finally get to the CD registration page to get the Steam key, the page talks about a 16 number key, not a 24 number... and then when you enter what you have anyway and press enter, the page closes and gives you no Steam key... You have to go back and press the registered button a second time to get it to display the Steam key.
Unclear and Dodgy... IMHO.
I don't know what ULS is, so that's lost on me. Whatever it is you don't need it to get your Steam key. The steps are clear, and I -- a 55yo guy -- was able to accomplish it without a hitch. If you're having trouble, I'd say you're being obtuse in some regard. Use common sense.