I watched a History Channel documentary on this, and the way it painted it, it was DEFINITELY ecumenism. I don't know how accurate it was, and the History Channel is not a very good source, but it basically pointed out how the "heroic example of these chaplains overcoming their faith differences" was a precursor, and helped along the whole interfaith-ecumenical movement in the postwar world.
I DO know that WWII was NOT good for Catholics. The priests who became chaplains had to work very closely with non-Catholics, and had to work very closely with protestants, rabbis, and others. They were essentially forbidden to proselytize, among other chaplains and among the men. They had to perform "bi-ritual" type stuff, because in a given comany there might be 300 Catholics, 100 Lutherans, 100 Methodists, 100 Calvinists, and 20 Jews, with only one chaplain, a Catholic priest. Thus, as the Catholic priest was forbidden to urge conversions (though he could accept converts should they come with no provocation from him) he was also made to perform Lutheran, Baptist, and other protestant services, because protestant preachers are merely laymen, not ordained ministers. This worked to the Army's benefit, giving them very flexible chaplains in the form of Catholic priests and Jewish Rabbis, but it obviously did not serve the faith well. Furthermore, any priest who refused to ecumenicize with the protestant preachers and Jewish Rabbis and stubbornly insisted upon holding to Extra Ecclesiam Nulla Salus was dismissed from the chaplain corps and sent home. This only happened to a few old priests (obviously the orthodox ones.) Furthermore, the chaplain corps was the first opportunity many of these men had ever had to speak with those of another faith. So effective were the pre-VII Catholic social structures that many Catholic priests had never before spoken with a protestant heretic minister, and were thus unprepared for the fact that these protestants were real men, and did not have cloven hooves and horns. The shared rigors of the chaplaincy led these men to become very good friends, and the liberal climate which infected society at the expense of absolute Truth in religion consequently led to the desire to "break down barriers" and say things like "Look how similar our religions are" instead of "Look at my Catholic orthodoxy and your heresy..." The priests who instituted these ecumenical gestures were thus committed to "reform," and eagerly anticipated a "new Christian order" of united Catholics and protestants after the war, because in this case, the walls which had been erected for hundreds of years, when both parties still believed in absolute truth, had just come crashing down. The priests became rising stars within the Church, many of them being elevated in the 1950s to the Episcopate, and participating in the liberal reforms of Vatican II, or not opposing the changes which it wrought in their dioceses and parishes.