Probably not. Reflection is a process that happens in the surface.

Think about mirror. It reflects visible light. Now if you paint it, does it reflect visible light anymore?

Heat reflectors are simply reflectors for infrared radiation. It’s similar to visible light but has somewhat longer wavelength (lower frequency).

If the paint is white, it’s far better than if it was black, but still worse than the bare reflectors. Anyway, white-painted reflector isn’t any better than a white wall.