From what I've read depleted uranium is not proven to cause cancer, nor is it not proven (With the exception that you inhale it or eat it).
In Iraq it's still up to debate if it causes cancer or birth defects, since burning buildings and other burning stuff also causes a lot of nasty things to humans.
From what I've read they were also used in Bosnia, and they haven't had similiar effects to Iraq.
So let the Ukrainians have their depleted uranium.