As per the documentation Blue Coat recommends the use of Administrator account to join the SG to a Windows domain. It is possible however to join the domain using a workaround without using an Administrator account. Blue Coat Engineering is investigating the ability for a normal user account to be utilized without using workarounds.
The reason the failure occurs when using a normal user account is because the SG is trying to set Delegation on the computer object after it is created in the AD tree. A normal user is not able to set Delegation and the error you see is:
In the eventlog you will find:
[LsaSrvProviderIoControl() /home/service-releng/p4/scorpius/sg_6_3/src/security/likewise/lsass/server/api/provider.c:112] Failed to run provider specific request (request code = 8, provider = 'lsa-activedirectory-provider') -> error = 1314, symbol = ERROR_PRIVILEGE_NOT_HELD, client pid = 0" 0 250034:1 sg_syslog.cpp:78