Yes, but generally for lies that they believe are true. Quite another thing to be willing to die for a lie if you are in a position to know that it is false, such as the Apostles were.
Discussion
Yes, they give a strong witness. I just meant, it's proof that they genuinely thought it to be true, but not absolute proof that it is true.
They claimed to be eye-witnesses of Christ's resurrection. That is the truth they were willing to die for. So yes, a very strong witness indeed. Could only really be explained away by a collective hallucination of some kind.
There is no absolute proof about many if not most historical accounts. Much of history is rough consensus