Harry can defeat Veritaserum (maybe), but definitely can't lie to a Legilemens - and the Wizengamot officially uses one to interrogate witnesses. Maybe they wouldn't do it on the spot, for whatever reason, but they would get to shortly, because this is very serious business. And if they saw in Harry's mind that he lied, they'd just interrogate him very thoroughly and then never listen to him speak freely.
However, it's likely that Lucius believes Harry is a perfect Occlumens, which means he would fight to block a Legilimency examination.
EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author's Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven, eight, nine, ten.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: