I think you need to do a little research on what you want to do, you are throwing out a lot of very different things:). I’ll try and clarify things, give you a kind of cheat sheet when it comes to music and so forth.
Majoring in music generally means one of several things. It can mean a BA degree on the instrument, which would mean taking lessons on the instrument, playing in orchestra and ensembles, plus theory classes, prob ear training, and obviously the general core courses. BA degrees often don’t require an audition, and from what I know admissions criteria are generally based on academic stats like SAT scores and such (and even in an audition BA, those stats still count heavily).
A BA in music can also mean studying academic music, like theory, composition, music history and so forth.
There also is the BM degree (performance), which has a very different focus. For one thing, most if not all of these are audition based, and while if the music school is located within a university things like SAT scores and grades will count, they will count towards admission to the university (and potentially merit aid), but for the music school admission for the BM is based pretty much entirely on the audition. You can be a 2200 SAT, 4.0 gpa, 10 AP kind of kid, get into the university, and not get into the BM program. Plus with a BM program, there is no such thing as there would be with a BA/BS degree, where you can easily change your mind, in a BM you in effect are declaring your major and forced to stick with it when you apply, which is different than a BA, where you don’t have to declare until after sophomore year. (In theory, in a BM you could switch let’s say from Violin to conducting, or Piano to composition, but I don’t think that happens all that often if at all)
The BM is very, very focused on playing, and a typical BM degree student will be spending significantly more time then a BA on the instrument in terms of ensemble playing, orchestra, lessons and so forth, it is a lot more intensely focused on the music (BM students in a university will also take the core courses, obviously).
In terms of being ‘easier’ to get in, I think it depends on what you mean. If you mean auditioning to be a BM student being easier, no way, competition for performance programs of any decent level tends to be tough. If you mean is a BA in music easier than studying something academically (like physics), I can’t answer that. And I don’t think (with one caveat I’ll explain below) that if you plan on getting a BA in music on Oboe let’s say, that it is easier intending to study history in getting in, in the sense that the admissions for a BA degree is in my experience not predicated on what you major in (with a BA , you don’t even have to declare your major until after sophomore year),so most of it is going to be on your stats, SAT score, GPA and so forth, rather than on what you intend to study.
The one caveat is that going into a college, music can count heavily in terms of being an EC, many colleges/universities look favorably on kids who play an instrument, both because of how they view music,. but also with an eye to getting kids to play in the school orchestras and bands and so forth. This would be true whether you plan on getting a BA on the instrument or not, it is more about it as an EC.
Which also gives you another option, if you like playing Oboe, there is no reason you could not get a degree in anything you want, and still be able to take lessons and play in ensembles and such, many schools have those opportunities for non majors.
In terms of whether playing the Oboe gives you an edge, that all depends. I have read the articles about how playing a ‘less desirable’ instrument (instruments like Viola, Oboa and Bassoon can fall into that) can help with things like admissions and merit aid and such, I am dubious about that, it is hard to say that is a rule. It all depends on needs, and if the school has a ton of oboe players, this wouldn’t help you much, or if it had enough bassoons or violas, same thing, and while there are relatively fewer kids playing those instruments (as opposed to violin), there also is a lot less need.
I agree with others, I think you need to think about what you want to do. If you love the Oboe and want to major in it,then go for it as either a BA or BM (the latter if you feel you are good enough), if you love the oboe but think you might like to major in something else, then major in that other thing but take lessons, play in orchestra/band/etc, and enjoy it:)…and rather than focus on what will make it easier to get into a school, do it because you enjoy it.