Anyone who uses Oracle Cloud is either directly or indirectly using Oracle Linux. Oracle Cloud is ~2% of the cloud market, so it’s small compared to the big three (AWS ~32%, Azure ~23%, GCP 10% according to this report) but 2% of a very big market ($237 billion total estimated for 2023) is still a significant user base.
From my own work, most of the Oracle Cloud adoption I see appears to be driven by favourable prices for Exadata Cloud as compared to purchasing on-prem Exadata hardware. Oracle Linux is also baked into Exadata “Cloud-at-Customer”, which has essentially the same cloud control plane but the hardware and all data lives on-prem at the customer’s site. That seems fairly popular with customers who want Exadata performance but can’t allow their data to leave their premises for security reasons.