No, most of the school's websites will say that completing a post-bacc program does not guarantee admissions into the master's program. Northridge is the only online program that I know of thus far that will automatically accept you into their online masters program if you complete their online post-bacc program.
I took the post-bacc program through San Marcos and it was biggest regret of my life. The professors aren't very supportive and personally it was a waste of money for me. I am currently in the second bachelor's program through ENMU and its been great, so that might be an option you can look into as well. I personally feel like if I need to take all of the prereq courses, I might as well take a few more classes and earn a second degree vs. a certificate of completion, but to each its own. However, I know that Baylor, Emerson, and NYU have fully online master's programs that will offer you the prereqs as apart of your graduate study. Best of luck to you on your journey!