As far as I'm aware you don't need SPNs. To connect from SAS to SQL Server we just specify IWA in the database connection string like so:
proc sql;
connect to odbc (noprompt = "server=MyServerName;DRIVER=SQL Server;Trusted Connection=yes;");
create table Want as
select * from connection to odbc
(---- Put your SQL Server query here
)
;
disconnect from odbc;
quit;
As long as you log on to SAS with the service account then the - Trusted Connection=yes - option does the authentication with the database.
If you talking about EG connections to SAS using IWA then indeed SPNs may be involved as @ChrisHemedinger describes.