That's surprising to hear I must say. Although I am not a Sheikh/Mullah I find that astonishing considering the teachings of Islam and the fact that organ donations are not mentioned specifically.
But all you basically need to know that it is "halal" is the following;
Surat Al-Mā'idah (The Table Spread) - سورة المائدة
5:32
Sahih International
Because of that, We decreed upon the Children of Israel that whoever kills a soul unless for a soul or for corruption [done] in the land - it is as if he had slain mankind entirely.
And whoever saves one - it is as if he had saved mankind entirely. And our messengers had certainly come to them with clear proofs. Then indeed many of them, [even] after that, throughout the land, were transgressors.
Or at least that should be enough if you ask me.
Anyway I have not really looked into this field in terms of the Islamic theology behind it but I am pretty much certain that as long as the person is dead and it can safe a life/be beneficial for a living person it is halal. Regardless of fiqh.