At the end, I couldn't actually think of anything they'd done to help, apart from making sympathetic noises!

You're right...

Well, maybe making sympathetic noises was emotionally significant to the Ood. Considering that none of these Ood had met any Friends of the Ood people apart from Dr. Ryder and he was undercover. And the Doctor was the only one who heard them singing.

I hope that they were just being polite, and that Dr. Ryder would also be remembered, poor guy.

Mind you, regarding the singing... if Donna could hear the singing after the Ood were freed, that means that the CEO's grandfather, who first enslaved the Ood, was even more culpable than I'd thought, because he would have heard the singing.
Unless he was particularly mind-deaf and dismissed everyone else's doubts as hallucinations. I can see that happening. But it still doesn't excuse him.

Oh, I missed the first one.

Donna mentions it in "Partners in Crime" as one of the weird things she'd been investigating.

there's something I could say, but it might be a spoiler if you haven't seen the season trailer.

I have deliberately avoided the season trailer.