Yes you can. Esri's Weighted Sum page provide the following usage details:
A useful way to add several rasters together is to input multiple rasters and set all weights equal to 1.
Input rasters can be integer or floating point.
The weight values can be any positive or negative decimal value. It is not restricted to a relative percentage nor does it need to be equal to 1.0.
The weight will be applied to the specified field for the input raster. Fields can be of type short or long integer, double or float.
By default, this tool will take advantage of multi-core processors. The maximum number of cores that can be utilized is limited to four.
If you want the tool to use fewer cores, use the parallelProcessingFactor environment setting.