Apologies, this has been a real comedy of errors. Our NetApp VAR spec'd the parts out for us and it looks like we've received the wrong stuff.
They told us we needed to add an "IOM12" module to the order to install into the FAS8020 since we only have IOM 6 ports on the controller (with 3 DS4246 shelves strung off the IOM 6), so we said "yea sure whatever" - so I was expecting that meant they were adding (what I'm guessing to be) a PCI-E 2x SAS 12GBps add-on card for the controller but nope, we got a X5720A in the mail which is for the disk shelf.
...So when we finally have the right part, I'm guessing we'll have to take a full outage if it is in fact a PCI-E card going into the slots shown here: https://photos.app.goo.gl/jC3UtnyAa2DgwXLt8. Not sure something going into those slots could ever be hot-swapped...