Karl_in_Calif once bubbled...
To my knowledge, which admittedly is not infinite, I know of no training agency that certifies new students who have never been certified before, with gear akin to a backplate and wings.
Now, correct me if I am wrong, or draw and quarter me, and hang me on a tree if I have misspoke.
Get out the paring knife.

My LDS is a PADI 5-Star. We'll teach and certify O/W students in a BP&W.
I see no reason to avoid using one for instruction. In particular, doing so complies with PADI guidelines. Its also a nice rig.
For the most part, the staff all use BP&W's. A couple use Dive-Rite TPII's. The rest use BC's.
Telling someone that they must take additional courses in order to use the rig is, IMHO, garbage. There is nothing in those courses that will teach you how to use a BP&W. Instead, you should learn all of the basics during O/W.