Well, first off, keep in mind that a wiki isn't a very reliable source of information. It's completely possible that the Legilimency thing was just the writer's interpretation, unless of course it cited a quote to prove this.
Secondly, I believe that the Hat was under a magically-binding oath to not reveal anything it finds in a student's head. That may just be my fanon mixing with my canon, though...
Thirdly, wizards look down on other sentient creatures that have proven countless times to have magic of their own, magic far superior to human magic. I highly doubt they'd believe a ratty, tatty, batty old hatty.