Nah, that's complete BS.
I did Vacation work with multiple people who weren't finishing the following year, some where Law/Commerce students who weren't finishing for a few years, others were 1st year or 2nd year of a 4 year degree.
If you're straight up with them, and say "I want as much experience as possible before I finish my degree blah blah blah" they don't care if you're not gonna finish the following year. As I said, they want GOOD people, regardless of what stage they're at.
I know of people that have been given offers for Graduate positions, when they're not graduating for another 2 or 3 years. It happens.