The big difference being, Nelvana owns (AFAIK) distribution rights to Di-Gata in the US and merely "sublicensed" broadcast rights out to 4Kids, meaning 4Kids probably couldn't have redubbed it if they wanted to, while Winx, AFAIK, was wholly owned for distribution by 4Kids, so it was treated more on par with their anime aquisitions.
So, this really depends entirely upon how the licensing works. If Rainbow SpA does what they did with Winx Club and grants 4Kids full distributorship of the series, then I can guarantee you it'll get a new dub because 4Kids is far to egotistical to use what already exists. But, if Rainbow SpA pulls a Marathon and decides to distribute this one themselves (as Marathon does with their shows, or as Toei was doing with Slam Dunk and Air Master) then 4Kids won't have a say in the matter - they'll have to air the tapes they are given since they'll only have broadcast rights.
Because the news article quoted in the OP is all phrased from Rainbow SpA's point of view - that is, it says "Rainbow SpA is selecting partners" and "Rainbow SpA has licensed broadcast deals with xxx and xxx", it leads me to believe Rainbow SpA will personally distribute the show in the US and has merely sold broadcast rights to 4Kids (and, for that matter, it could very specifically be for CW4Kids meaning 4Kids couldn't even shuffle it over to 4Kids TV if they wanted) meaning 4Kids will pretty much have to use Rainbow SpA's dub. Which, based off Winx Club, is a very, very good thing.