I've been looking through the ArcGIS help documentation in order to try to understand my options for creating rasters with rectangular cells, as well as to identify where processes may fail to take account of input rasters with rectangular cells. I'm not sure if I've yet got the full list (can anyone add to it?), and also I've come across what appears to be a bug with one of them (details below).
Ways to create rasters with rectangular cells from scratch:
a/ Create a numpy array and use arcpy.NumPyArrayToRaster, specifying different x and y cell sizes.
BUG: While this creates an arcpy.Raster in memory which has the appropriate cell dimensions, nevertheless when you save this raster (using the save() method of arcpy.Raster) it reverts to square cell dimensions.
Ways to create rasters with rectangular cells from existing rasters:
a/ Resample Tool
b/ Project Raster Tool (or ReProject function) EDIT: While this accepts a "Cell Size XY" Parameter, I notice that its help documentation states that it will only output square cells
c/ Split Raster Tool
d/ Rescale Tool
Ways to store rasters with rectangular cells:
a/ As almost anything other than an Esri GRID
b/ In a Mosaic Dataset
Gotchas with processing rasters with rectangular cells:
a/ Spatial Analyst operations are based on square raster cells (see What happens with rectangular raster cells in Spatial Analyst? | ArcGIS Blog )
b/ Many other raster operations will resample to square raster cells - especially where they use the Cell Size Environment setting, which can only be set to a single value.