Actually DO's are considered independent applicants. Independent applicants include DO's, IMG's and Canadian's. The stats on match rates are all figured individually for these independent applicants by the ACGME.
The figures on success in the AMA match for independent applicants is misleading however, particularly for DO's. See, US born MD's are required to go through the match, but, independents can sign contracts with programs prior to the match. This is actually fairly common, particularly in primary care specialties and with DO's. Program Directors have an incentive to fill their programs with US grad's as renumeration from Medicare for these residents is higher than for IMG's. DO's are considered US grad's, plus they can sign up prior to the match, thus securing good resident selection and not leaving things entirely to chance in the Match. In my medical school class, ~25% of the grads doing ACGME residency signed contracts before the match. Those spots taken by those who signed contracts before the match were disclosed as not matching when the stats were run by the ACGME. So, these figures can be misleading.
As far as doing an AOA intership, be careful if you plan to do an MD residency. This was discussed earlier. The AOA year may not be accepted by the MD program and you may not be eligible for funding for the last year of the MD resicency. Funding for residency spots is a big deal to Residency Directors and lack of funding for one year could make the difference between being accepted/rejected to a program. If you are interested in doing a residency that requires a preliminary year (i.e.: anesthesia, some ER programs) then doing an AOA internship prob'ly wouldn't be a problem, but, double check with the residency program first.
Right now I'm going through the process of trying to obtain approval for my first year of AMA residency towards the AOA internship requirement. It has been a difficult process. Suggestion: if you are at all interested in practicing in one of the 5 states requiring an AOA internship, do one. If not, go to the best residency you can find.