Lol no you're not going to want to delete everything in your tmp folder. You need to keep things such as mysql.sock and aquota.user/quota.user.
Do the followingin SSH to see what is so big and then more then likely it will be safe to delete that.
Do you have eaccelerator installed or something? If you do, I've noticed eaccelerator seems to not clear its cache from the tmp folder and just seems to leave it there. You can create a crontab to empty the eaccelerator folder if your tmp folder fills up often and it is because of this.
You may need to use a command called tmpwatch which removes files which haven’t been accessed for a period of time. Normally, it’s used to clean up directories which are used for temporary holding space such as /tmp.
Following code will remove all files/dirs from /tmp if they are not accessed in last 2 weeks (24 * 14 days = 336)