Answered my own question
I tried a trial transaction for a Superstore gift card with an empty prepaid card I had in my wallet, just to see if it would even allow me to enter a prepaid MC number.
Of course the transaction didn’t go through.
I then received an email from them
We are also unable to accept payments using an American Express and/or a prepaid credit card (ie. Prepaid Visa)
Damn, that was short lived