As an Imperial fists player I must say that it would suit the lore. But as for your original idea of White Scars. I know i have around 20 or so transfer sheets from the years with White scars decals, and I'm sure you can find them online for a decent price. Here's one listing that can give you an idea of the prices you'd be looking at.
Your current scheme is a little too close to the Soul Drinkers which could work in your favor. You can dual purpose them as both traitor and loyal marines. I mean I'm sure its only a matter of time before we start seeing traitor Primaris Marines which puts you ahead of the curve.