Within Spain, this is a valid arrest warrant. Why would you think that Spanish officials would not enforce it? On the political front, Zapatero has said enough totally idiotic and openly anti-American things that I suspect he would be more than happy to watch the Spanish legal system put these GI's on trial.
Like in every other democracy there is a strict divestiture between the executive and the judiciary in Spain. Therefore Zapatero had no influence on this mad judgment. Furthermore it would be political suicide for him to enforce it, since he would have no backing of the other European nations for such a step. Europe has its soldiers in active missions in Iraq, Afghanistan, the Balkans and many other places on this world. If European courts would prosecute American soldiers (no matter if this would be justified or not), it is very likely that US courts would prosecute European soldiers in return. I am sure that it wouldn't be a problem to find reasons on each side... Besides that most European nations are interested to keep the transatlantic relations calm.
This are the reasons that nobody (not even this moron Zapatero) has any interest to validate this crazy judgement. Just one more needless insult. We all would be well advised to fix the stressed relations between America and Europe instead of wasting emotions on insignificant idiots like this judge.