Will Dullcote get rid of small scratches on a model painted with gloss?
I doubt it. Dullcote will actually make them show up more.
About the only way you can get rid of them is to sand them out. If you want to keep the gloss finish and avoid sanding you could try Future floor polish if the scratches are real small. Future levels itself really well and can actually fill really small scratches but you might have to apply more than one coat. And even then you may have to do some light sanding with a fine grit or maybe even a polishing grit.
Dullcoat will reduce the visibility of very fine scratches, but if they are really that visible, they will be visible even after dullcoating. Cleaning up with fine sandpaper (1000 or 1500) before dullcoating would be a better bet. Be very careful of sanding over decals, however.
Also, you might try filling the scratches with paint. This requires either a super fine brush and excellent brush work, or the tip of a sharp toothpick. At worse, you’ll have to sand it if you apply too much paint, but then if you don’t try that, you’ll have to sand anyway.