Usually if it's a rejection based on potential inadmissible issues such as employment reference problem (unable to contact your employer), traceable report from RCMP, or medical-related issues, the CIC procedure requires VO to send you a "Procedural Fairness Letter" to offer the applicant a chance of appeal and your application will never reach "decision made" process if there is any rejection.
However there are cases that VO are allowed to send a direct rejection without procedural letter. For example, if there is NOC mismatch or missing "permanent" keyword if you have LMIA, there might be straight rejections after DM (we have seen some cases on the forum).
Above are information I collected based on CIC operational guideline and this forum. Other members are welcome to comment.