Good question!
90% of what I’ve done is actually from the unreal marketplace cause I’m simply not artistic enough to make most of the stuff myself.
I DO know that if you use anything from the marketplace in your mod that you cannot work with anyone else on your mod or you’ll break the EULA agreement.
(nobody else can have access to edit any of the marketplace assets)
Even if it isn’t against the ‘rules’ I’m sure it will be taken into consideration due to ‘originality’ and such.