I think Rossi's bloviating blog entries could be admissible as evidence. It just takes one witness to say that that's what Rossi said on his blog. Then all of his blog stuff would be admissible. I'm surprised IH's lawyers haven't already angled in that direction.
Generally speaking, statements made by the opposing lawsuit are not considered hearsay. So IH can probably get Rossi's blog statements in fairly easily when Rossi is on the stand, by asking him about the statements.
However, the statements in question must be relevant - which means that they have to have a tendency to show that a fact that is of consequence to the case is more (or less) likely to be true. So not all of the bloviating is likely to be relevant.