OK, the Netziv (R. Naftali Tzvi Yehudah Berlin) never actually wrote about blogging. But his nephew, R. Barukh Epstein (author of Torah Temimah), wrote about his uncle's championing collaborative communal learning. Granted, this was in regard to learning in partners of two but I think it is clear that it is also relevant to blogging.
The following excerpt from R. Epstein's memoirs, Mekor Barukh, was sent to me by a reader for another reason. This was translated in the controversial partial translation My Uncle, the Netziv that, interestingly enough, was translated by R. Moshe Dombey, of Targum Press.
Here is my loose translation of the relevant passage:
At every available time, he would talk about this matter in general and would say that in his view, anyone who learns on his own, anyone who clarifies a halakhah on his own or writes a book on his own, without the assistance of friends and students, almost certainly makes many more mistakes than a person normally would according to the principle of nature "Who can discern his errors?" (Psalms 19:13), since when he errs no one informs him of it. Therefore, he remains in his mistake and, frequently, one mistake leads to another and a simple error causes a fundamental error, all from the source of one single [original] mistake.