Awhile back, Onthemainline posted an interesting excerpt from HaMelitz that records what is supposed to be a conversation with Sdei Chemed. This report was spurious and in Igros Sdei Chemed V. 1 pg. 113 there is a letter from his students protesting this libel against their Rebbe.
I noticed the following piece in the memorial volume for Sdei Chemed, Chemdas Yisrael that state that Sdei Chemed would quote and argue with the writers of HaMelitz and HaTzvi (perhaps the cause of the libelous piece posted by S.). The writer claims that these pieces were removed in later editions.
Although I do not have access to a first-edition Sdei Chemed and cannot validate this claim. In a periodical of this same publisher (Sovalski) Knesses HaGedolah there are two very interesting Teshuvos of HaRav Sdei Chemed. On pg. 63 he writes:
הרב המו״ל יצ״ו אמר שכבר העיר ע׳׳ז הרחז״ס בהצפירה כי הכלים האלה דין כלי זכוכית להם עכ״ל ואני לא ראיתי דברי הצפירה בזה (כי אין נמצא בעיר הזאת רק אחת אצל תלמידי יחיו ושאלתים ולא נזכרו אס יש בזה בהצפירה ולא אוכל לידע איה מקום כבודם לעיין בזה)
and on pg. 44 he cites HaMagid and HaTzefirah so it seems that Sdei Chemed had no problem quoting the Haskalah writings in the context of his Teshuvos.
I also noticed a letter of Sdei Chemed in regards to Yishuv Eretz Yisroel here (I do not know if this was republished in Igros Sdei Chemed). This is likely why he was willing to permit his students to eulogize Herz'l (I cannot identify the opposing Ashkenazic R' SA)