People who don't think Flair would be helpful to Ziggler obviously didn't see how much good work he did as a heel manager with AJ Styles and Beer Money in TNA (Before management tanked the angle), plus he was superb as the manager/leader of Evolution, adding but not detracting from Batista and Orton as they were just getting their first big push into the spotlight.
Unlike in the Evolution Days Flair can no longer wrestle regular matches, even on the reduced "Legends" schedule WWE used for him and HBK back then. There were long stretches of time during the Evolution angle however when Flair wasn't wrestling at all and was strictly a manager and mouthpiece which worked just fine.
The only drawback with Flair as a manager is the audience predisposition to cheer him, he was over as a heel with Evolution but outside of that it was almost impossible for WWE to get the audience to cheer against him, Flair turned beloved Mick Foley into a heel with ease and even got significant cheers when he was with Evolution in matches against Shawn Michaels. Still, I could see it working to give Ziggler added attention, especially now with HHH promoting Orton as the "Corporate Chosen Champion", playing on the fact that HHH recruited Flair to be his mentor and manager to take him to the next level, and Orton relied heavily on Flair to kick start his career as well, Flair coming in at Ziggler's behest to help him get over HHH & Friends could set him up either as a rival heel or as an opposing face, depending in how they play it.