A few thoughts. Although I agree that a RAM disk is probably the fastest way to run a VM, I personally decided to use an SSD for some obvious reasons, e.g. less risk, no copying required, less expensive, ...
The reason why Workstation prevents you from creating a snapshot is safety. Since a snapshot can grow up to the size of the provisioed disk size, Workstation checks for a certain amount of free disk space. You can disable this check in the .vmx file (mainMem.freeSpaceCheck = "FALSE"), but I would not recommend it. Regarding snapshots, these are no temp files but files which grow in size depending on virtual disk activity. Placing them on another location (e.g. a HDD) wouldn't make any sense, as it would slow down the VM. All virtual disks in a snapshot chain are used! (see http://kb.vmware.com/kb/1015180)
André