Youtube – Dissociate YouTube channel from Google + account

No there is no way you can do that. This kind of restriction is not only for YouTube Channel names but also for email-addresses from all service providers and many more.

Is it possible that whoever hijacked the YouTube account attached said account to their own Google+ profile? The YouTube account seems old enough to have that happen to it as it likely was not attached to a Google+ account when you made the YouTube account.

If so, that means it's attached to another persons email account (or Google+ account) that may be the student or hijacker in question. You would need to contact Google and see if they can reattach your Google+ to the YouTube account, but I don't know how they could verify that.

I've worked in customer service. If it's clear the YouTube channel is on the topic of your employer, then you or someone in management would need to prove they are who they say they are to Google (normally by faxing a copy of their drivers license to the service provider). Then you could be able to retain the account based on copyright alone as the channel is using your employers copyrighted information. If not, you should AT LEAST be able to close the YouTube channel or get the videos removed by filing a copyright infringement report. Then start a new channel and take better care of your security next time around.