So I found the issue. Didn’t have to go into Unreal – this is a Skeleton issue.
So in the skeleton of the character, the wrist joint is oriented different than the Mobu controller. I’ve attached a pic from Maya of the baked skeleton.
You’ll see the wrist bone’s orientation is off center, even though the wrist is visually pointed forward. Rather than messing around with this offset value in Unreal (trying to fudge perfect value for the weapon), I would highly recommend making an ‘attachment’ bone off of the wrist for just this purpose. You’ll have fine control over the weapon placement and get it just right. It’s super handy down the line if you ever want to animate the weapon flying out of the hands too (or any other crazy moves like that).