I would support adding the English word, since it seems to be missing, but you probably need to check several dictionaries, both AE and BE, to see how the compound is written, as one word, hyphenated, or as two words. My own impression is that roll neck could only be the noun, not the adjective, analogous to crew neck, polo neck, etc.
I personally think I would write
He has a crew-neck/rollneck/polo-neck/turtleneck sweater. (adj.)
This sweater has a crew neck / rollneck / polo neck / turtleneck. (n.)
As for what it is, I'm not sure how accurate Wiki is here. At least, I would say rollneck / roll neck is also used in AE, mainly for a loose style of turtleneck, sort of halfway to a cowlneck / cowl neck. (Anyone remember those? Was that the 1980s?)
And polo neck isn't the same thing in AE, is it? I thought it was the much shorter style that doesn't turn over like a turtleneck, just a round close-fitting knitted collar. But wait, maybe that's a crew neck ...