I suspect the gripes in the comments/eplies to that post are not problems, or are common to any kind of third party commercial platform, but it's definitely worth checking the TOS closely, whoever takes Tumblr next, to make sure it's not a Fanlib type company.

With, again, not knowing anything about PornHub specifically, at first glance I agree with you -- it's probably the same copyright claim language that every website makes in order to display content, but a careful reading of the ToS will be required. Sale of a content hosting site always requires that level of caution, at the very least.