Two thoughts on this for AACOMAS:
1. Submit early without the MCAT. AACOMAS still requires a verification time period for someone to go over your transcript and verify it (AACOMAS is generally way faster than AMCAS, often taking days to weeks when AMCAS is taking weeks to months). AACOMAS also typically transmits in the mid-June, which is much earlier than AMCAS. Therefore, submit to only one school that you likely wouldn't go to anyway (often called a throwaway school) since you don't have your MCAT score. Your application will be verified and ready to go the day you get your MCAT back. If your MCAT score is good, add it to AACOMAS and add the DO schools you want to apply to. If it is bad, walk away from the application/the one throwaway school you submitted to and you won't be considered a re-applicant at the schools you really want to apply to. You can reapply in the future to those schools with a better MCAT score.
2. Assuming you have everything ready to go besides the MCAT, submitting June 22 is still super, super early for the DO cycle. This way you can fill out the application and just wait for your MCAT. If good, then submit. If bad, then you never applied/paid for anything and won't be a reapplicant anywhere. Even if it takes AACOMAS a month to verify your application, having an application sent out to DO schools in Mid/Late July isn't going to hurt your chances at DO schools. DO schools interview way longer than MD schools and offer straight up acceptances (not waitlist spots pending an opening) far longer than MD schools.
Ultimately, if you are a truly competitive candidate for DO schools, the difference between choosing 1 or 2 is going to be having a potential shot at getting an acceptance in September-Nov (option 1) vs Oct-Dec time range (option 2). Grand scheme of things, both of those are still early acceptances in the cycle. Basically, it won't make much of a difference.
For AMCAS, the answer is always submit to a throwaway school since verification can start to take near months later in the cycle and MD schools fill up faster than DO schools.
Regardless, make sure you submit your transcripts to AMCAS and AACOMAS as soon as the application opens! It takes AMCAS and AACOMAS some time to match transcripts to applicants (and this also takes longer throughout the season). You don't want to submit only to find you need to wait another month for you transcripts to be received before they even put you in the queue for verification.
FYI: AACOMAS doesn't automatically receive your MCAT score. You need to send it from the AAMC's website to AACOMAS and that can take a day or two to get it in AACOMAS.
