Resolution:
A unix machine's PAM setting may be configured to prevent Engine Daemons from runing authentication completely. Following is the minimum setting for Unix Engine RunAs to work.

/etc/pam.d/other:

#%PAM-1.0
auth     required       pam_warn.so
auth     required       pam_unix2.so
account  required       pam_warn.so
account  required       pam_unix2.so
password required       pam_warn.so
password required       pam_deny.so
session  required       pam_warn.so
session  required       pam_deny.so