There is, but that not big of a difference. Let’s make a distinction first.

There are really two situations in which you hire contractors: staff augmentation and expert help.

With staff augmentation, you’re hiring a contractor because you just need more hands. Your contractors probably a look a lot like your FTEs and you might even convert one to FTE from time to time. With expert help, you’re hiring a contractor because of their specific expertise in a certain topic–an expertise your team lacks or isn’t up-to-speed on.

If you’re hiring for staff augmentation, treat the interview like an FTE interview. If you’re hiring for expert help, treat them like a vendor–ask for client references/testimonials, prior example work, etc.