Then Rome would have to agree to married clergy would it not?
Institutional reunification is perhaps possible with some Anglican and Lutheran factions, but it seems to me that the bulk of these denominations is heading toward less unity with Rome, not more. I think realistically, we'll see more individual conversions from Protestantism, but while those are happening, the trajectory of all Protestant (in the broad sense) communities of faith will continue to be centrifugal.
I believe traditional Anglicans and some Missouri Synod Lutherans were moving toward RCs, while I concur that the evangelical Lutherans (Dr. Tiller's church) and Episcopalians are probably moving away (especially after the homosexual acceptance issue in the ECUSA). It really is sad because I believe firmly that it is God's will to have a unified church of Christ on earth.
Most protestants regarded Pope John-Paul I, John XXIII and Paul VI as well as John-Paul II as real ecumenical leaders. I do not believe most feel that way about Ratzinger.
I often wonder about the current pope, as with John-Paul II there is documented evidence that he intervened on behalf of Jews in Poland during the Holocaust. I take Benedict at his word, as I do with other Germans of the period, that they really did not fully know what was going on during Hitler's regime. Still, there is that nagging suspicion of why didn't they when the Nuremberg Laws were so conspicuous?
Rome never disagreed with married clergy as practiced in the Eastern Catholic Churches (Greek Catholics, Melkites, Maronites, Ruthenians, etc), and in Eastern Orthodox Churches. Priestly celibacy is uniquely a discipline of the Latin Church, but not of the entire Catholic Church, and, I am sure, will remain in the Latin Church forever. It was never an objection raised by the Orthodox.
it is God's will to have a unified church of Christ on earth.
Most definitely it is God's will (John 17). But the union cannot be syncretist, purely formal union based on some vague commonality of belief in divinity of Jesus. Jesus's prayer was that we be one as He and His Father in Heaven are one. This means that unity should be of essence. With the Orthodox, some Anglicans and some continuing Lutherans I see such possibility. With the rest, the possibility is nil.
real ecumenical leaders
Most Protestants understand ecumenism as mutual recognition, intercommunion, prayer events, that is, external signs of union, while maintaining differences of doctrine. The Catholic understanding of ecumenism is conversion into doctrinal oneness. For example, we consider ourselves both Orthodox and Catholic, and we consider the Eastern Orthodox in essence Catholic. A similar essential unity exists with the Anglican Catohlics. Should the Eastern Orthodox also come to see themselves as both Orthodox and Catholic, we will have reunification. In that light, there are certain gestures made by some popes and not by others that look as if the Catholic Church might fall into indifferentism, and these gestures are seen as "true ecumenism". That is a wrong way to look at things. They are simply expressions of commonality of some ideals and some goals. They were not meant to lead to some syncretic super-Church.
About the role of the Church during the Second World War, I refer you to many solid books that explain it; since I haven't read a single one of them, I won't recommend any specific book. The topic could easily fill several FR threads as well.