Like rich2202 said, you need to swap RX and TX between destination and target (you may have already done, it's just such a common pitfall with UART, that it is worth mentioning again.).
Pin 8 should be connected to the middle pin on the 232 port, Pin 9 should be connected connected to the inside pin on the 232 port (with the outside pin being ground).
Start with trying the attached vi - it should just read whatever the pi sends and print it to the control where you can see it.
Private message or email me and I'll send you my contact info, we should be able to get on the phone and get this figured out.
here is a link to a project I did that read a ps3 controller on the host computer and built up a string of commands to send over a comm port to an arduino (there's a lot of overhead, and I directly used the Visa library - what the Serial palette calls into - so there's not a lot of obvious parallel, but this is also not the only project I've done with LabVIEW talking over serial, just the most relevant, since I had communications going both ways).