Marking as not trusted in Lion seems to work fine. When I open DigiNotar's own site[1] in Safari, I get a "can't verify the identity..." dialog popup. Not sure how to check if it's an EV cert, though it'd be surprising if they're not using an EV cert for their own CA site!
Also works in Chrome...
[1] https://service.diginotar.nl/files/DigiNotar%20Root%20CA.crt