A German carrier could indirectly increase British Pacific strength

Would Graf Zeppelin prevent Britain from lending carrier strength to the United States in the Pacific?

Not necessarily; the German threat might produce a larger British carrier fleet, potentially leaving ships available for Force Z or early Pacific battles.

The American comparison begins with a correction: USS Saratoga, rather than Enterprise, was the operational carrier in the situation raised by the commenter. A German carrier would tie down British assets in home waters, but it would also make a British carrier-building pause less likely. That larger force might provide air cover for Force Z or allow one or more British carriers to appear at Coral Sea or Midway. Graf Zeppelin could reduce Britain's immediate freedom of deployment while increasing the number of carriers available later.