D5 Render 2.4+ has a "Convert to D5 Asset" feature. Use this on your imported free models to turn them into "local assets" so you can scatter them using the Scatter Tool . That is a game-changer.
Good news: D5 Render supports . You are NOT locked into only using their proprietary assets. d5 render assets free download
The Ultimate Guide to Free D5 Render Assets (Where to Find Them & How to Import) D5 Render 2