Did Saruman Believe He Could Master The One Ring?

[Boromir88]

I'm sure the Witch-King did give Sauron an account of Frodo and the whole adventure leading up to his horse being washed away in the flood. But, as was discussed earlier in this thread...did Sauron get a good image of what Frodo looked like through the WK's description (if indeed there even was a description given)? Would Sauron be able to tell if Pippin was Frodo or not? The phantom showed quite reasonably that the palantir did not paint a 'clear picture'...again Sauron didn't even know the palantir was out of Isengard anymore...how clear could the picture have been? How clear of a picture did the Witch-King get of Frodo? Afterall the encounter took place at night. Why would Sauron want to not only remember Pippin's face, but Pippin's voice? The question still remains what else is it that Sauron wanted from Saruman? Or what he wanted from Pippin? What else did Saruman's captive have that Sauron would want immediately?