When I use the scene.useRightHandedSystem = true; my imported objects still have -Z , where in my 3D program I had +Z.
Is my understanding correct that the useRightHandedSystem is supposed to reverse that?
yes if you are importing a gltf object and setting the useRHS BEFORE loading anything we are not supposed to change anything on your meshes
So how would I ‘fix’ the -Z on the meshes? I noticed that with RHS true what happens is the root Z scaling changes to -1.
It’s not a huge deal for me to fix this, but I would like to do it for clarity in my workflow 
This should not happen, unless I am missing something. I also assume the scene is set to RHS right when created (and not after the model is loaded). Would you be able to reproduce that with your model on the playground