Im going to go to a Ivy with my army rotc scholarship (non-stem). It will be, obviously harder to get top grades there than at stateu. So it would stand to reason that going to a harder more competitive college would negatively impact my GPA. If I want to serve active duty, is this something I should be concerned about?
Don't be too quick to assume that getting top grades at a StateU is easier, it all depends on the school and the student.
That being said, as stated in previous posts you could be attending a school with grade deflation which could impact you GPA.
The school you attend and the degree of difficulty in grading does not have any effect on your OML, a 3.3 is counted the same no matter where you go.
While it's true you shouldn't start worrying about accessions before you start school, it's not wrong to consider the things that will effect you when the time comes.
I agree with you, don't jump to a major based on what you might do in the future, be smart in your decisions but study what your interested in and do your best with what you select.
I guess to answer your question directly, if the school you attend is known to deflate grades and the average GPA is low, then yes, this will have an effect on your OMS score that will in the end determine whether you get active duty or not.
Best advice is to really hit the books hard and do your best, keep a high APFT and be active in your Battalion.
Best of luck.