Thank you for the info and tip, GarryP.
It's funny about the Scribus warning that an SVG "might contain unsupported features". It says that every single time, so I never even think twice about that, any longer!
Your suggested work-around seems to be the best choice. However, the problem there is that controlling Scribus's "Free Radial" Gradients is a huuuuge pain in the butt. Do you know if there is a simple blur option in Scribus, as an alternate work-around?