A Google fight (excluding Chinese) turns up 549,000 results for 草食系男子 and 571,000 for 草食男子. Much closer than I expected, but the 'kei' is definitely not required.

I think they meant that http://thelongandshort.org/issues/season-three/images/DeskHe... has the 系 but then the translation the article gives below it is missing the "kei".

Oh, I see! Yeah, that's true.