You will definitely need to find out if the cameras really do have the same MAC. But the sticker is just that, a sticker. I bought a couple of Dahua branded cameras off of AliExpress, and for two of them the sticker was just wrong.
I purchased many dahua cameras from Aliexpress- box serial number tags don't always match chassis serial number tag, and some chassis tags didn't match firmware serial number tags. Hasn't been an issue but I suppose if I were ever going for a warranty repair, I would think it would be an issue.