Translation:They know her but they do not know him.
UTON is not a word in Swedish, we have utom and utan. Supposing you mean utan, it is only used after a negation. So De känner inte henne utan de känner honom is a correct sentence, meaning 'They dont' know her, but they know him'.
utom is used like this: Jag tycker inte om någon utom honom 'I don't like anyone except him'.