I'd stick with Idye Poly when using a vinyl mask. Worm dyes contain acetone, which can attack the adhesive of the masking material, making it more likely to bleed.
That said, I've done spin dyes with the (Spike-It) black worm dye, and had mixed results. Seems to be better for Champion type plastic. It acts much like a Sharpie, and can leave a film that will smear. I end up wiping it with alcohol to remove the residue of the black worm dye. After that, it has held up well. Still, I prefer Idye Poly.
Peace,
-Jeff