From the ALSA wiki
NVidia do not produce cound cards but their motherboard chipsets do provide a PCI bus interface for audio chips mounted on the motherboard. As a result they can appear to be Nvidia sound cards. See Sound Cards: Introduction for details.
NVidia use a PCI bus interface which is very similar to that used by Intel. As a result the NVidia interfaces can be driven with the intel8x0 alsa driver.