At our school we've got the chance to hire on a percussion instructor and there are two people in the running. A snare player from 2005 Cadets and a chick that was the pit section leader sor Southwind. They're both pretty cool, but which one do you guys think we should go with?

I think that you left out the most important choice.
The instructor that best fits your program. Who cares where they marched..Just because they marched with so and so doesn't mean that they are good instructors. And it doesn't mean that they will be the right choice for the job.
I hope that you are not going to make that decision based on where they marched.. but rather make the decision on what each of them can offer the program and then choose the best fit for the job.
Here's an example.. I know a high school that has a Director that marched Blue Devils for 8 years. And I know another school that has a director that never marched a corps before. (The talent pool at both schools are relatively the same.) Want to take a guess which school won every time they competed against each other. (Hint: not the BD alumni's band.)
So my choice is
The instructor that best fits your program.

Well, more than one years experience within a program really can make a difference in the individual. I say more than one year because its easy to understand the aspects of a successful program after one year, but after more than one, those aspects will become more of a second nature.

Just another thing to think about...especially if any procedures of the mentioned corps programs would conflict with how your band program operates. (For instance: If one of them uses a certain punishment method not acceptable at your program.)

There's many things to consider, but Bill really hit it on the head...I just took it a step forward by telling you to analyze the cadets' or southwind's operations that these prospective instructors are familiar with, because those things may create conflict with your program.

I agree with what is posted above, all are good points.

I would look into several other factors as well:

1. What other playing/educational experience do they have? Are they studying music in college, if so where?

2. What other teaching experience do they have? Have they worked anywhere else? You should think employment history, or would they be recommended by their last employer to another?

3. What is their plan for the group and is it compatible with the Director's current and future goals. For example, does your director see this person doing any work with concert percussion, an indoor line, private lessons, etc.

Those are just a few more things to think about. If you have a choice, then ask as many questions as possible so that you will hopefully come up with the best fit for your group!

NL