Seeing how it is almost 1 am and I am getting ready to switch shifts, I am up and will try to give some headway without being a MASTER in this particuar area.
The rating scheme can be determined by many factors including the positions you hold and who is above you.
Being the Supply SGT, I would assume that for your unit there is no one over you, i.e you are the PSG for the supply/HQ platoon? IF you have an NCO above you, then they should/could be your rater.
However if you are the top of the food chain for your platoon then it is possible to have the XO be your rater, as with most supply/HQ PLTs the XO is your first line supervisor. If this is how it works in your unit, then thats what you should Drive On with.
Additionally, there is nothing wrong with Officers being your Rater/Sr. Rater. Being Intel myself, my raters for the past few years have been officers. Just make sure that you and your fellow NCO COrps "helP" write the NOCER properly and with your best career interests at heart. Make sure SNCO's take a look at it, and ensure the LT does it properly, so having a crappy NCOER written by an O1/2 wont hurt you down the line.