Is there a software/extension to convert an SLD to Esri. lyr format, or to import the SLD directly?
If SLD is declared you can get layer parameters with parsing XML.
In ArcGIS you need add a local feature class and load it as feature layer. Next, identifying type of symbology of your layer in SLD and next generate symbols with appropriate type in ArcGIS. Finally save your symbology to LYR.
I don't know if this script is dev... I find lot of subject for convert LYR to SLD but no reverse.
You can do a script for this conversion with arcpy and xml packages in Python environment if you want. I think lot of persons are interested in.