In English, both are correct depending on the context of the sentence. However, a Team that Works is significantly different with a group that has Teamwork...in order to drive the true spirit behind the word, it is best written as a single word.
Hate them or Like them, in a lot of ways, the Americans are the pioneer in "Teamwork" where it's most obvious through their team sports starting from as early as 1900...more than a century ago...