Here's an interesting read on the subject. It's geared more toward hiring lawyers but I think it's applicable here.
Personality Tests in Employment Selection: Use With Caution ? Cornell HR Review
I've heard of people having their spouses or even others who have already passed the Hogan take the test for them. There's no way United can prove you took the test. Just another hoop to jump through. Very frustrating when you've already been an airline pilot for 10+ years with no problems at all and you don't "fit the bill". They are turning down a lot of good people.
Apparently when United decided to use the Hogan test they gave it to a bunch of management and training pilots to take and set the baseline. People who volunteered with no jeopardy to their job (Ie no pressure). So maybe just put yourself in the mindset of a senior company go-getter pilot when you take it. I've heard from a few United recruiters to "be consistent." One even told me the answers don't matter as long as you are consistent. He said he's taken the test a bunch times for fun.
Seems like a lot of fails on the Hogan. I've heard 30%. It's too bad they don't let you take it again right away to see if there's a fluke. You know, since the test is so infallible and all...