If they're using serialized EPCs (which track a unique item, not just SKUs) then this won't work because need to ensure each physical item is uniquely tagged, and that two tags with different serial numbers aren't on the same item (though duplicate tags with the same serial are fine) and that no two items have tags with the same serial.
If they're using non-serialized EPCs (so just logging SKU) then they need to ensure exactly 1 tag is on each item - no more and no less - otherwise inventory counts will be inaccurate.
Unique tag serial numbers would work fine. No duplicates (don't even understand how that would happen). More than one tag not a problem (enter one or all; whatever, as long as scanning later identifies the one item).
If they're using non-serialized EPCs (so just logging SKU) then they need to ensure exactly 1 tag is on each item - no more and no less - otherwise inventory counts will be inaccurate.