When R. Yaakov Kamenetsky zt”l was Rosh Yeshiva of Torah Vodass, students used to help him prepare his house before Pesach. One group checked for chometz the seforim that might have been brought to the table. The work proceeded without event, until one bochur let out a shriek, having discovered a copy of Mendelsohn’s famous (infamous?) and ground-breaking German translation of Chumash, known today simply as “The Biur.” While there are likely fewer students in Torah Vodaas today who would know about the Biur and its author, that particular bochur did, and his horror was visceral. Rav Yaakov immediately understood, and reportedly smiled (he seemed always to smile) and said, “They are surprised that I would own such a work. If only they knew how many difficulties it helped me solve.”
Although not an irrefutable proof, the following excerpt (Emes L' Yaakov YD 281) would seem to falsify the above to some extent:
The ruling that the Biur should be left in a place where it will rot ought to preclude the possibility of R Yaakov owning a copy himself.
Even in his famous permissive ruling allowing usage of the Jastrow dictionary, R' Yaakov does not appear to be exceptionally tolerant of heresy. He writes (YD 246):
I assume R Yaakov was told that Jastrow was the head of a Reform congregation which would render him a heretic, although at that time being connected with the Reform movement was not necessarily synonymous with heresy (as can be seen from the wiki entry on Jastrow).
The distinction made between Torah and lexicography seems somewhat difficult. According to this, one can learns the following Talmudic passage Kesubot 17a:
מאי הינומא סורחב בר פפא משמיה דזעירי אמר תנורא דאסא רבי יוחנן אמר קריתא דמנמנה בה כלתא
without reciting Birkas HaTorah (but see the commentary of Rebbenu Chananel there) and there are many other passages in which lexicography is of great value.