The most popular answer to "Can something be hacked?" is: With enough time or resources anything can be "hacked". Security is only as good as it's weakest link.
Skype uses encryption for any type of communication it processes (256-bit AES). It is more than highly unlikely encrypted video calls would be intercepted by a third party due to Skype hosting your video call. The most susceptible component in your Skype communication (other than you) are the computers themselves. If your computer has a virus, malware, or other 3rd party software explicitly designed to remote in, monitor or screen capture your active desktop, then your communication can be intercepted in that fashion. Otherwise you should feel rather confident that your communication is secure and not freely open to prying eyes.
You can check out Skype's security center if you have more questions on Skype security: