i didn’t looked that up in lsb or posix doc, but to my understanding
tmp is stuff that is very temporary and shouldn’t survive a reboot
/var/tmp/ is temporary but should be able to survive a reboot
So /var/tmp/ is barely more important that /tmp, (depending on your usages, it may actually be very important).
I like how this was last sentence very confusing ( my advice : dont delete it, dont backup it either)
You said you re backing up TO /var/tmp (not from). For me that s no place to store urbackup files, /var/liburbackup, /data/urbackup, /opt/urbackup, that would be better places.
Do not tell me you re backing up from and to /var/tmp.