Yes, you can animate your own lower poly game models with it either manually or via BVH (which Studio imports) and you can export to OBJ or purchase their FBX exporter for use in 3DGS (although I don't know how reliable that plugin is). It's simply a matter of preparing a model (see below), and importing it.

You are also allowed to use any 2D output (renders used for sprites or whatever) in commercial applications.

If you want to model and skin/texture, you can use Carrara and MAYBE Hexagon 2. I'm guess Hex has an exporter given it's th same company, but I'm not sure. If you're clever you can rig your model to work fully with Studio's tools, and create many variants from some general purpose models via the "pulling" and "pushing" sliders just like when you are creating a custom character from Daz content.