The federal government in Germany attempted to ban crucifixes in schoolrooms in Bavaria, but the Bavarians refused. We'll see if the Spanish are as Catholic.
Not to sound too hopeful, but the King of Spain has as much constitutional power as Generalissimo Franco did. In other words, it's not a purely ceremonial office. Often on state occasions, a major address to be given by a high-ranking clergyman would have to be cleared by the King, if not in person then certainly by His Majesty's master of ceremonies and protocol. So, I'd say there is a pretty good chance that there is profound disagreement with Zapatero's agenda "at the highest levels."
He may be digging his own political grave. Now is not a really good time to support a dilution of Spanish national culture.
Well, this may seem like a reversal of our usual roles, since you're generally more pessimistic and I'm generally more favorably inclined towards contemporary royals, but to be perfectly honest I wouldn't count on King Juan Carlos, who is widely respected (even by republicans) for swiftly and voluntarily surrendering his powers in order to "democratize" Spain after Franco's death, to resist Zapatero's agenda, even if he did approve of that cleric's address.
For one thing, I'm not sure how devout a Catholic he is. King Baudouin of the Belgians temporarily abdicated for 24 hours rather than sign his name to the bill legalizing abortion in Belgium in 1990. But King Juan Carlos has never made even such a symbolic gesture. When Spain legalized abortion, Catholic writer Frederick Wilhelmsen wrote wistfully, "If Juan Carlos had defied the government and the constitution by calling in the Armed Forces to back him, what would have happened? ... Don Juan Carlos would have appeared before the entire Christian world as a Catholic king and knight whose sword was at the service of the unborn." Needless to say, no such dramatic action was forthcoming.
King Juan Carlos has been a popular, dutiful, dignified, and effective constitutional monarch, and I respect him for that. But I see no sign that he has any desire to be anything more.