How does a "neon tester" work?
An excellent question.  

High voltage DC will work if there is enough ground leakage from person to ground.
If the resistance to ground is about 1 megOhm it should work with DC above the neon strike voltage.
At 10 megohm it may work.
At above 10 M it's uncertain.

Have you SEEN it work with DC yourself?
What voltage DC? 
What environment - bare feet? rubber shoes ... ?