So I'm too late to give you an answer for this jam, but for the future:
I can't speak to the technicality of the rules, but I think covering a copyrighted piece of music would be in violation of the spirit of them, at least. Public Domain or CC-licensed music, on the other hand, no problem.
There's some great classical stuff in the public domain. Disasterpiece used Chopin's Prelude, Op 28 no 4 (aka "Suffocation") to great effect for the ending of Fez. He even admitted in an interview to just finding a midi file online and orchestrating it with synths. Chopin in particular has I think a bunch of short pieces that would work well for video game music, especially among the Preludes collection.
Something to think about for the next jam.