Yes. But the reason it's not listed as a requirement on the
300 visa website is because the online form that is listed is the 40SP.
"You can lodge your sponsorship form online after your partner has lodged their visa application and given you their Transaction Reference Number (TRN) or application ID."
That form is the 40SP. Complete that and you do not need to upload a second one via paper and scan. Just do the online version.