Volume rendering is a visualization technique. Output of volume rendering is a 2D color image. No data is generated that could be used for FEA. See detailed explanation in this topic:
For FEA, you need volumetric mesh or at least a surface mesh - represented as Model node in Slicer. You can create model from a volume by segment the volume using Segment Editor then export the Segmentation node to Model node.
@Michael_Hardisty Could you comment on this? Were you able to use Cleaver extension after all? Have you checked how difficult would it be to upgrade Slicer’s extension to Cleaver2?