About ArcSys doing 3D, well if they did Guilty Gear Xrd Rev story with Unreal Engine 3. Animation is in 30fps I believe, so it still look not as smooth in some parts. However, since they move on to UE4 with Dragon Ball FighterZ and new incoming Guilty Gear, everything looks much more improved.
Wasn't there an anime last year about humanoid gem or something that use a similar animation style? Pretty well received too iirc.
It's Houseki no Kuni (Land of the Lustrous) by
Orange studio, they have Beaststars as their current CGI anime for this season. But as you know Japanese anime studios, they mostly do adaptation and rarely do original project. In this case, even if you give RWBY to the studio, the show is still plagued with horrible writing from original writers.
The other anime studio I know usually do 3D/CGI is
Polygon Pictures, they did Ajin and Sidonia no Kishi (Knights of Sidonia).
Edit: Add example of using UE3 for Guilty Gear, noted times.
Around 0:05-0:08, walking animation isn't great. And the fight starts at 4:58, it looks quite "skippy" and not smooth.