Has Oura sleep tracking accuracy been independently validated against real medical devices? From what I've seen, all consumer wearable devices give inconsistent data and none are really what you could call accurate.

Yes, there are several studies. One is this [1]. I have not tried the Oura 4 myself but once I test it I can compare with other devices. Clearly sample=1 but I found big errors with some watches.

[1] "Accuracy Assessment of Oura Ring Nocturnal Heart Rate and Heart Rate Variability in Comparison With Electrocardiography in Time and Frequency Domains: Comprehensive Analysis": https://pmc.ncbi.nlm.nih.gov/articles/PMC8808342/