I think if you had specific circumstances that dictated you had to take online courses, you would probably be okay. I agree that it's probably not a huge deal to a lot of schools, especially in the current application environment.
For me -- having had a lot of experience with undergraduate students who would take summer courses or online courses outside the major -- the key issue for me is whether the course itself has the equivalent rigor as the home university. A lot of online/summer courses, especially in prerequisite science, tend to be for non-science majors and fulfill general education requirements. However, the courses themselves would not meet prehealth rigor (for science majors). I would normally go back to the syllabus for specific classes to determine this, especially if the home university didn't approve transferring the grade or credit. Of course, I also know a lot of universities run "hybrid" classes as a mix of in-person and online for prerequisites, so the issue of "online" courses isn't a clear "don't do it" unless it comes from a non-accredited university.
Yes, the DAT would make a little difference, but you didn't really disclose that you had taken the DAT (I presume your 30 in OC is hypothetical), but the DAT is not the same thing as a traditional final exam in a class. For me it just tells you how strong your test-taking skills are for a science-rigorous test, not necessarily how well you did in your class. Otherwise there would be a stronger correlation between grades and MCAT/DAT/etc. scores, which I can tell you there isn't a linear relationship.
The pain will come with having to enter all your transcripts into ADEA AADSAS. Get unofficial copies of all your transcripts and accurately transcribe them into your application when it's time.