3D models can be used as particles in a particle generator. There are two things that need to be done. In the particle generator definition, set the particle stage's type to one of the pt_model flags. The following would make the stage use particle model number 13:
Type = "pt_model13";
In the particle stage definition, remember to set a color for the stage. If the color is not specified, the default values will result in a completely transparent particle model.
The model definition must have a matching ID. For example, particle model number 13 uses the following ID:
ID = "Particle13";