If he is, I don’t think we know this. He’s at the stage of being able to block veritaserum, and thus probably to put up a block to stop anyone reading his mind, but I don’t think we’ve been given any indication that he’s reached the point of being able to show false thoughts to someone attempting to read his mind.
I would add that he knows Voldemort is probably alive. If he were to testify by placing his memories into a pensieve, he could show that the Hogwarts inner circle has strong reason to suspect that Voldemort is alive and behind this plot. This might create a measure of doubt among the Wizengamot, at the cost of probably throwing the country into turmoil, so we can call this the Stupid Sentimental Hero Option.
We should also make an account Harry’s capabilities
Can create a Patrunus 2.0
Partial Transfiguration
Knowledge of Muggle Science
May have Lucius convinced that he is Voldemort
Is a part of the Prophecy, though only Dumbledore knows this
Is an almost-perfect Occlumens
Has non-public knowledge about Dumbledore and Quirrell
Not much use if he hasn’t figured this out.
If he is, I don’t think we know this. He’s at the stage of being able to block veritaserum, and thus probably to put up a block to stop anyone reading his mind, but I don’t think we’ve been given any indication that he’s reached the point of being able to show false thoughts to someone attempting to read his mind.
I would add that he knows Voldemort is probably alive. If he were to testify by placing his memories into a pensieve, he could show that the Hogwarts inner circle has strong reason to suspect that Voldemort is alive and behind this plot. This might create a measure of doubt among the Wizengamot, at the cost of probably throwing the country into turmoil, so we can call this the Stupid Sentimental Hero Option.