Hey, welcome to the boards!
I'll be applying this fall as well... perhaps I should give bad information... 😏
Haha. I wouldn't!
1. You could but be prepared to explain in detail WHY you decided to pursue vet med instead. And, the only place to really mention it specifically is in your personal statement, so you might think about how you'd work that in... but the interview people would notice that you worked at a hospital and may ask about it, so be ready to explain either way. If you don't mention it in your PS, you'll probably still be okay. Just keep working on the experience now. If you come in with over 500 hours plus a GPA like that and good/great GRE scores, I think you'll still be in good shape.
I also would like to mention, slightly off topic, that if you are ONLY applying to OKSU, you don't have to use VMCAS! I'm glad I did because now, for my second go round, I know what to expect (and I'm applying to several places). BUT, you can save money if you're only interested in OKSU. They have some other way to apply. You would need to contact the admissions ladies for more info, though. I see that you said "highest hope" so this may not apply to you, but i just wanted to get the info out here while I was thinking of it.
2. A little large animal experience never hurt anyone! If you could manage a bit of diversity there, I would recommend it. However, with a GPA like that and a good GRE, you might be okay anyway. So, don't freak out about it, but try and find a place to shadow or volunteer just in case.
3. No, no, no. While there is a bit of rivalry there, obviously, OKSU folks are going to recognize that OU is a great school that has a great education system. No on is going to pick or not pick you based on the color of jersey your football team wears.
Good luck, and don't forget to study for the GRE, good test-taker or not. There's also the biology GRE to take, and that's a bit harder to study for (more material, but things you should have learned already) so don't forget about it. They only do those in April, October, and November, so you have a while before you have to worry about that.
Let us know if you have any more questions. 🙂