My guess: some are, but it depends a lot on their priorities, schedules and circumstances.
Some companies which were already running CentOS 8 when CentOS Stream was announced may have stuck with CentOS 8 as long as they could. Red Hat forced their hand much earlier than they'd promised -- end of 2021, about 2 years, far short of the 10-years of support updates enjoyed by prior releases.
Some folks paid up and went to RHEL 8, some switched to AlmaLinux or Rocky after they came available; others made the bigger transition to a SUSE, Ubuntu or Debian, assuming they stuck with Linux.
The companies which were still on CentOS 7 likely stayed there, for the most part. But their EOS time is coming up next year (2024), and some of them will be making similar decisions as the former CentOS 8 folks.
My guess is some places using CentOS 8 in R&D or test environments may have shrugged and simply use CentOS Stream when the time came. They presumably don't much care about Red Hat support contracts. Companies that deeply care about vendor support and are willing and able to pay for it are likely running RHEL all along.
Overall, I suspect the churn and uncertainty Red Hat has caused with their actions around CentOS, Stream, and now RHEL source, are probably not leaving the majority of customers feeling comfortable and complacent about long-term use of RHEL.