Sysadmin role is required according to the documentation:

/SQLAUTHentication=INTegrated | SQLuserid
    This parameter specifies the authorization mode used when logging on to the 
SQL Server. The integrated value specifies Windows authentication. The user id 
you use to log on to Windows is the same id you will use to log on to the SQL 
Server. This is the default value.

    Use the sqluserid value to specify SQL Server user id authorization. The 
user id specified by the /sqluserid parameter is the id you use to log on to 
the SQL Server. Any SQL Server user id must have the SQL Server SYSADMIN fixed 
server role.

http://www.ibm.com/support/knowledgecenter/SSTFZR_7.1.4/db.sql/dps_ref_opt_backupoptional.html

This message and any attachments (the "message") is intended solely for the 
addressees and is confidential. If you receive this message in error, please 
delete it and immediately notify the sender. Any use not in accord with its 
purpose, any dissemination or disclosure, either whole or partial, is 
prohibited except formal approval. The internet can not guarantee the integrity 
of this message. BNP PARIBAS (and its subsidiaries) shall (will) not therefore 
be liable for the message if modified. Please note that certain functions and 
services for BNP Paribas may be performed by BNP Paribas RCC, Inc.


Unless otherwise provided above, this message was sent by BNP Paribas, or one 
of its affiliates in Canada, having an office at 1981 McGill College Avenue, 
Montreal, QC, H3A 2W8, Canada. To the extent this message is being sent from or 
to Canada, you may unsubscribe from receiving commercial electronic messages by 
using this link: www.bnpparibas.ca/en/unsubscribe/ 
<http://www.bnpparibas.ca/en/unsubscribe/>. See www.bnpparibas.ca 
<http://www.bnpparibas.ca> for more information on BNP Paribas, in Canada.