I think, and i'm open to alternative theories, is that using RAM instead of disk is safer when the tmp directory fills up.
If you have /tmp being a regular directory on your root drive, if you fill your disk witg tmp files, other processes wont be able to save files to disk, resulting in lost data.
If you have it in a ram disk, when the tmpfs fills up too much, the oom killer can get more space (unsure if oomkiller can wipe tmpfs, but that probably would be ideal?).
Neither are good, and both can result in data loss, but tmpfs may be safer?
Are you thinking rowhammer? My understanding is limited, but doesnt rowhammer require being able to write to memory at a consistent address, co-located with the data being attacked? Im not sure thats doable with tmpfs, but probably worth an investigation by someone more knowledgable than me :)