I just happened to be looking at some ni-cd charging schematics and info today... from what I read, it looks as though charging a nicd battery in reverse is a pretty sure way to kill it. that's part of the reason it's good to condition the individual cells once in a while, because sometimes one cell will get discharged before the others, but current will still be flowing through it, so it will actually start to charge in reverse from the other cells... which usually kills it.
you can try charging them again normally, but I wouldn't get my hopes up if I were you.