Other than a teshuva in Shevat Halavi and Yabea Omer, I haven’t heard or seen the oppinions of current Gedolim on the Shalit prisoner exchange. Does the Rav know if there was a consensus amongst Ashkanazi Gedolim on this matter?
The silence of many Rabbanim is not by chance, and it is not only because they prefer to stay out of the politics of this difficult question.
Although many “right-wing” rabbis objected to the deal, claiming that it was a danger to Israel (in spite of the clear and present danger to Shalit’s life), this decision is not simple, and it is impossible to make it without knowing all of the security details and assessments.
Of course, the threat of other soldiers/civilians being kidnapped and ransomed is a halachic concern, but the fundamental distinction between the times of Chazal and today is that today the army is able to respond and to take action to prevent or deal with future kidnappings.
There are also many other complex considerations involved, and a Rav cannot really address the issue without knowing them all in depth.
I believe that this is the basic reason why most Rabbanim have not expressed an opinion on the exchange.
For a general analysis of the issue, see our article http://www.dinonline.org/2010/11/25/a-halachic-perspective-on-modern-day-ransoms-too-high-a-price/.