There is a similar rule mentioned on page 44 of Codex IG (new).
Since there already is such a rule for the new IG, i don't think that the WD rule is intended to apply to them. That rule from page 44 (not exactly a rule but a unit option) seems to be supposed to replace that WD rule.
Technically, there are no restrictions in the validity of such WD rules though (unless it's optional or there are restrictions mentioned there), but you won't make many friends if you insist to use a "questionable" rule.
A forum community dedicated to Wargamers, Wargaming 40K enthusiasts. Come join the discussion about Warhammer and Wargaming collections, miniatures, tactics, terrain, reviews, accessories, history, displays, models, styles, scales, reviews, accessories, classifieds, and more!