I've worked for a government data center where they ran instances of Ultrix in a commercial VM to run old data processing software that ingested and barfed out CSVs that contained UUencoded blobs of image data. All this was written in a mixture of very
very old Perl, shell scripts in some gawd-awful Ultrix shell CSH script, and C code full of weird -isms that made it difficult to port to anything made after the rise of mammals. This was of course mission critical. At least they virtualized it instead of continuing to run physical Ultrix boxes, which was apparently a
huge fight with management.
A side dish of LULZ was that they were experimenting with moving the VMs to EC2, so there is probably Ultrix in EC2 now.
This stuff is really, really common in large "mature" industries and government.