I think this kinda stuff always creates a two-tiered team, so it shouldn't be relied on as a way to hedge anything. You get the A-team/"our people" and the B-team/"their people" and right from the start everyone knows this. Then there's differences in pay, benefits, and expectations, etc. In other words, to use interns or contractors as a potential employee filtering method, to me, just sucks. I haven't seen that work well.

But, but, but! If you're looking to give people a chance to learn and expand, with no future obligations, internships are definitely the way to go. The key point being: an intern that doesn't turn into an employee is not a failure.

Take someone who doesn't even know what they can do and put them with a great team, part time, with real responsibilities, and with the idea that they're there to help out and learn and see if anything happens. Usually, it won't. If it does, great. If they become a future employee, excellent! My career was built from this, but it requires an employer that's willing to take a risk.