This label could be used interchangeably with spiritual Satanist as they are, but also aren’t, mutually exclusive.
A polytheistic Satanist just means that you believe in Satan as a literal being, but you also believe in the existence of other spiritual beings, and/or gods. You could be a spiritual Satanist who works with the Norse gods/goddesses or the Greek pantheon which would be polytheistic Satanism.
You could be a traditional devil worshipper with Satan as your chief deity, while honouring and working with the daemonic divine. This would too be a polytheistic view as you are spiritually connected to more than one deity.
This identification describes someone who acknowledges Satan to be a high being or God as well as honouring or working with other spiritual beings. This applies to any combination of pantheons. If you are a religious Satanist or Devil Worshipper, I don’t think it is necessary to call yourself a polytheistic satanist on top, because it is a given that you will honour the demons in your practice. Adding layers of labels is confusing for everyone and it over complicates things, but of course you can identify in whichever way you feel is needed.