Yes - Oasis montaj and Target would significantly outperform Target for ArcMap when rendering in 3D. For one thing, Target for ArcMap is a 32-bit application, whereas Oasis montaj and Target are 64-bit applications. While not a major differentiator, 64-bit does helps with being able to support larger datasets (esp. voxels).
The main difference comes from the fact that we have been able to optimizes Oasis montaj and Target in ways that were not possible in ArcMap. In fact, with the release of Oasis montaj and Target 9.8, we are introducing some major improvements to 3D rendering.
Note: if you are a Target for ArcMap users and your looking for increased performance, you may be interested in Target for ArcGIS Pro. Target for ArcGIS Pro works with Esri's ArcPro and utilizes all the 3D rendering capabilities and enhancements that ESRI has introduced recently. Target for ArcGIS Pro and Esri's ArcGIS Pro are also 64-bit applications. That said, you should notice a significant performance boost between Target for ArcMap and Target for ArcGIS Pro.