I'd bet its becoming increasingly popular/convenient to do so with the growth of container-based test suites - really trivial to include a "postgres-ram" image for your test stack instead of one that uses disk, and you don't even need to know what tmpfs is to do so.
If the tooling you use lets you create tmpfs mounts for your container its very easy, yes. AFAIK those are RAM-backed by default. I think from inside a container it could be difficult to have the permissions necessary.
