"However, the Solaris guys tell me /tmp actually means something to the

OS to say that all files in /tmp are memory mapped files and high
access rate files. "

For UNIC systems, /tmp indicates temporary storage that is not
guaranteed to persist after a reboot. Some unix'es clean up /tmp -but
AIX doesn't.
The default setting in AIX is to create a small disk-based filesystem
for /tmp, and the rest of the directories are hosted by larger
disk-based filesystems. Off hand, I can say that /tmp/probably doesn't
get journalled. if you are using jfs2.
If your customer wants the files in another directory and you want to
improve performance of that filesystem, you can change attributes of
the filesystem using chfs command.

regards
-kamal