There's many ways to represent it, but the "sub" in "subpixel" does tell us that someone along the way needs to deal with fractional pixels. :-)

It does not imply fractional glyph positioning though. By itself subpixel rendering simply exploits knowledge about the configuration of the subpixels (red, green, blue) of the pixels on a particular raster display. (horizontal, vertical, what order,... ?)