What's an african dorf frgs?
Anything with soft skin (kinda like our fingers) will make for easy chompings by the turtle and very painful if not deadly results for the one being chomped. If it doesn't eat the frog, it will definitely maime it terribly. And, like SpotsMam already pointed out, a lot of amphibians have toxic poison glands that could kill your RES. I wouldn't chance it.
I have several types of frogs that I maintain in their own habitats. They require both water and land where they don't have to worry about being run over or chased by the turtle. Also some frogs like to climb and benefit from a taller enclosure. You could setup another display for your frogs and newts to live peacefully together. I really like the ExoTerra Glass Cages for those kinds of displays...
http://www.blackjungle.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=BJTS&Product_Code=PT-2607&Category_Code=T
I'll try to post a pic of mine later...