Yes, HP-UX 9.00 and later include a RAM disk driver. The driver is NOT officially supported by HP for customer use.
RAM disks can waste memory space.
RAM disks aren't saved over a reboot, and require special action to do so. You must write a C program to delete them from a running system. You must first purchase and install the optional OnlineJFS product, the advanced bundle for the VxFS file system. This enables a number of extra mount options for VxFS filesystems. There are two versions - RamDisc plus and RamDisc classic.