Well, both Steve Urkel and Spongebob are spoken by Santiago Ziesmer in their respective German dubs, so your assumption is correct. ;) Concerning Carl however, he and Mr. Krabs are spoken by two different voice actors. Carls German voice is Helmut Krauss, whereas Mr. Krabs' is Jürgen Kluckert.
That's what Steve got after all of the furniture he broke in Carl's house and not to mention all the haywire experiments and disasters. I wouldn't doubt Uncle Carl and Laura would love to see Steve Urkel and Eddie and/or Waldo in boot camp. lol ;-D