We have used 5 models of Noritsu printers, and other than the MP1600 (old model) which was 400 DPI, all models I am familiar with are 300 DPI. I could not find one that is 320 DPI on Noritsu's website... Not saying there isn't one, but since most of them share the same laser/imaging subsystem, seems strange they would throw a 320 dpi one in the mix. I really do not believe there is a 320 DPI noritsu printer.
As far as moire, I think they may be blowing some smoke at consumers, they are telling them to not size to 320 dpi because they believe there printer is 320 dpi ... doesn't make much sense.
We've been producing digital prints on various photo printers since the early days of Kodaks CRT printers,and all digital output on fixed ratio output devices like this (dye-sub/ LED/Laser) that we've used we size the the print to a 1-1 pixel ratio ... image size equals output size. We currently have 140 studios and photograph over 1 million sittings a year, producing over 8 million 8x10 prints. Moire is something that we only see as the result of the raw file demosaicing process.
These printers work very differently than inkjet ... instead of a series of various color dots in various sizes, each pixel can contain any color within the printers gamut. There can be a true one to one relationship.
If you send a print to this printer that does not match its 300dpi resolution, I believe all it will do is resize it. It does not go through the same process as an inkjet printer ... it will just resize it.
So personally ... I would prefer to resize them myself and have complete control rather than let the printer do it.