Hello robmiggs,
We 3D modelers mostly use 3ds max or Zmodeler for GTA 4. I guess Blender would work if you can export as either .obj or .3ds. Zmodeler can open those files, although I suggest exporting in .obj format, it makes things alot easier.
We use 3DS max to make the model, and we do the converting in Zmodeler.
Although some people make and convert stuff in Zmodeler.
So the answer to your question would be yes, as long as you can export the 3D model(s) as .obj or .3ds
I hope this answers your question!!!