You cannot use a negate if the ability is prevented.
So if FS enters battle first and negates KoT before he enters battle, Platinum_Angel's statement is correct in that KoT would not be able to negate FS (as he is prevented).
If KoT enters battle first and THEN FS is played, KoT prevents the negate on FS, and thus it does not have the desired effect.
Note that if the card in question were CBN or CBP, then its negate would still function (as it could not be prevented in that case).
