Hi Dave,
Do you have ASE exact version (select @@version). Also, post the output from sp_version, just from the Script value " OLEDB MDA Scripts".
I tried ASE 16.0 SP00PL03, using 16.0.0.2 Provider and my test worked okay.
I did create the table on mssql either as nullable or not null. In all cases I was successful in the bulk copy.
My thought is something is out of whack in the metadata - ASE Provider calls sp_oledb_columns to gather this information.
Also, provide the version info on MSSQL Server and the DDL for creating the table in case there is something there.
Cheers,
-Paul