The shop I'm doing my DM with is OK with DM using BP/W as part of the class because they want the students to be exposed to several different gear configurations. I think this makes sense from a teaching aspect and a business aspect:
- Not everyone in the OW class will have "primary + octo" especially if they are diving with their own new equip, which could include an array of configs, including BP/W, Air2, etc
- Not everyone in the world that you might dive with will have the "student" setup used in a class. Best to be exposed to all the different types of configs early on in case you buddy with someone with a different config than yours
- Not everyone who starts diving knows what gear they want from the get go, so by exposing the students to a wider range in the class an LDS is more likely to help students see what's out there and make up their mind.
Typically the instructor will wear "the student rig" in order to demo the skills, and if the DM is wearing something different (7' hose, Air2, whatever) the instructor will then point out the differences in the configuration and then ask the DM to demo.
This is especially useful if someone in the class has the same gear as the DM, because they can see how it's done.
When I did my OW there was a guy in the class who bought all his gear prior to pool sessions. He had an Air2, so the instructor made us all buddy with him at some point to see how the skills - esp OOA - would be done with that setup. Very smart, because you may end up as a real buddy with someone with that config someday.