Ok. Wait. Something is not right.
Have you talked to them and see if they print spot inks?
Here is a screenshot of their personalized decks:
The ones from the right are most likely digital prints, which definitely will not use spot inks. (They will probably use RGB files).
A company that big will probably not use spot inks because this slows down the ...
In single color printing blurry effects such as glow or drop shadow the color of the effect should be set only white (=paper) or the used print color.
The effect settings contain also blending mode. It should be = normal; other blending modes can behave differently than with CMYK or RGB colors.
If you expect the effect blur around object A be visible on ...
If you want to go down your workaround route using the black plate, I think you'll need to speak to your printer to check it's OK with them. There's no reason why it shouldn't work technically. A plate is just a plate - it has no colour until it's inked on the press. Edit: See note in comments
BTW "Computer to Plate" isn't a fully digital printing ...