I assume you meant OD school, not DO school. I just computed the average GPA for all 17 OD schools, including PUERTO RICO. The average GPA came out to be 3.33. This is a litte lower than MD school with ~3.5-3.6 (I'm not sure exactly, too many to figure) and only slightly lower than DO school with a 3.41. For all these schools you have to remember the GPA is an Average!!! That clearly means students with lower GPAs get is too. The range of those accepted is 2.2 (Puerto Rico) up to 4.0. To have a decent chance you really need a minimum of a 2.7. I would guess for those who gain acceptance with less than that have something really amazing about them. With a lower GPA the OAT could help you by over shadowing it.
In reality, OD school is "easier" to gain admissions to than MD school. That does not mean you can have a 1.5 and get in. You still have to have a respectable GPA. The average GPA is lower, but only about 30% of those who apply to OD get in. I don't have any data to back this up, but I always thought about 50% of those who apply to MD school get in. People have made argument both ways about which is "more competitive," but it is really just how you look at it.
You can also boast your app by shadowing an OD or 10. I lucked out and my Dad is an OD so I have been working for him since I was 16, now 22. That really helped me. I also worked for an orthopeadic surgeon over the summer. That showed the school that I have looked into other fields and still applied to OD school. For the last 1.5 years I have been doing research at a medical school and I volunteered at a hospital for a semester last year. I'm also on the committee who is planning Drake Relays. Relays is internationally known track event and is also like our school's Homecoming. The funny thing is that I only ran track in 7th grade and could really care less about running, the student events are fun though.
There are student who did more than I did and also those who have done less. If you have a family or have been working a job to help pay for your schooling, the schools do not expect you to have tons of extras. They understand the strains of life. However, if you have only been taking 12-15 credits a semester and have no extras (job, clubs), they may be a little more critical of your app.
Above all, shadow an OD to make sure that is what you would like to do.
Hope I helped a little.