The shop that I did my OW training in did not pay instructors except in store credit. That led to the instructors getting a lot of nice, new equipment regularly and since it was a PADI shop, many of the instructors from that shop now use that equipment to instruct independently (the shop closed when the owners retired 5 years ago). The shop that I DM at does not pay DMs for assisting with certification courses if we are planning to become instructors, but we do get paid (barely) for teaching snorkeling classes. I recently learned that DMs can teach ecology classes, but I haven't asked how the pay for that is to decide if I want to pursue it along the way to OW Instructor. Instructors get paid $45 or $50 per student for classroom and pool and not much more than gas money for doing checkout dives, but there was some talk late last year about making some changes to that because doing OW checkouts is a lot of work. One of our instructors lives part time in Florida where he said he gets $150 per OW student.
All professionals in good standing with the shop get their insurance covered and professional fees repaid each year, as well as SSI React Right course every two years to maintain CPR, First Aid, and O2 certification. We also get "key man" pricing on any equipment sold in the shop, which can be a pretty significant discount.