I actually haven't witnessed the caudos eating planaria. I figure that if they do eat them, there would not be so many in this particular tank. They even seem to avoid the bloodworms that are taken over by the planaria. There are many more planaria than can be seen in the above pics, mostly in the gravel.
I've played with the idea of introducing danios to get rid of the planaria. I'd first have to look into temperature tolerance for the different danio species. But I'll be moving in December anyway, so that would be a good time to transfer the newts to a new tank and leave this one to dry out.
Pamela, thanks! Ed, no worries on that score as I haven't been blessed with the same good fortune as Paris. Benjamin, the biggest are around 1 cm, I guess.