Sure, but in the USA it's actually really hard to incite violence in the eyes of the law. For example, when it comes to USA laws, Trump almost definitely did not incite violence. But lots of people would disagree with the statement that he didn't incite violence.
But the statement was "inciting violence is illegal". Which involves the law. That's a different question.
And an impeachment trial is not an Article III court. Nor is it intended to be. It is inherently a political proceeding and not a criminal trial. As such, ethics and morals are certainly at issue and the rules of Article III courts are not relevant.
Nor did the founders intend[0][1] them to be criminal trials. Which is why someone who is impeached and convicted is not immune from criminal prosecution in an Article III court.
Here's a lawyer's video on the subject: https://www.youtube.com/watch?v=XwqAInN9HWI
"President Trump’s conduct on January 6, 2021, followed his prior efforts to subvert and obstruct the certification of the results of the 2020 Presidential election. Those prior efforts included a phone call on January 2, 2021, during which President Trump urged the secretary of state of Georgia, Brad Raffensperger, to “find” enough votes to overturn the Georgia Presidential election results and threatened Secretary Raffensperger if he failed to do so."
https://www.congress.gov/bill/117th-congress/house-resolutio...
Impeachment may be shaped like legal process, and the final act may be called a “trial” and supervised by the Cheif Justice, but its a political process, and the difficulty of proving things “in a court of law” is pretty much irrelevant except to the extent that comparisons to a court of law may be provide political rationalizations for actions in the impeachment or trial process.
(IIRC, one version of the bill of impeachment had a second article related to Abuse of Power with regard to the Georgia election call, but that was eliminated in favor of making the issues regarding the call part of the context for the insurrection charge, rather than a separate charge.)
Proving criminal liability is not required[0] in an impeachment trial.
According to the Ars piece, Amazon claims that Parler users were planning violent attacks openly on the site.
That may or may not be true. I guess we'll just have to wait until the archive[0] is fully released.
If it is true, that might be incitement, but it's definitely conspiracy. And since folks died, it's quite possible that at least some folks could be charged with Felony Murder (discussion here[1]).
But we obviously won't know until we can get our greasy little paws on all those messages, photos and videos.
[0] https://threatpost.com/parler-archive-amazon-suspension/1629...
[1] https://www.lawfareblog.com/felony-murder-and-storming-capit...