I see your point, but I don't think cremating them would solve all the problems your suggesting.
First off, its almost always the case that the group in control of a dead body are the victors in the battle. So if your side defeats the enemy, you don't want to cremate their bodies because you want them for research. Only in cases like Asuma's death would they even consider cremation. But since Asuma was able to be buried in Konaha, within the barrier, there was no real reason to cremate him. Not to mention, that battle was a fluke anyway, considering pain recalled Hidan and Kakuzu. If he didn't do that, all of those Konoha soldiers would have died.
Your other point about Edo Tensei can also be worked around even if a body is cremated. We know that Kabuto almost certainly did not infiltrate Konoha and steal Asuma's DNA from his grave. Rather, he almost certainly gathered some of his blood from the battlefield that he was killed at, therefore cremating a body surely does not erase all existence of a body, leftover blood being one of them.
he must have been pretty zealous to dig some graves.
