Perhaps the OP added that to Wikipedia. Or got this idea about Yekkes and Oberlanders from reading Wikipedia. Or from the same source as that website got it. But I’ve never heard that. And it is common knowledge that not only are the Oberlanders currently very closely aligned with Chasidim (as can easily be eyewitnessed by walking through almost any Oberlander neighborhood) on the religious spectrum, but that for centuries many customs of Chasidim and Oberlanders have had great similarities.
The Rema was accepted by far more than just the Yekkes right from the get-go. And not all of frum German Jewry were Yekkes. There were other hashkafos and customs among non-Yekke German Jewry.
(Shoutout to squeak.)