Great question!
Yes.
For the game competition they've recently revised the rules as follows:
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Rules Addendum II: Non-Team Asset Work Contrubution
If other students who are not directly on the team want to contribute an asset, but do not want to contribute on the team itself..
- Out of team assets from students are allowed as long as the total non-direct team member additions to the project are less than 10% of the total project itself. This includes all aspects of the game, and everyone who has worked on it must be credited, along with their contribution.
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And we're honoring that rules change in the film/animation competition as well (IIRC rules haven't been formally updated yet, but consider this formal notification).
Just want to re-emphasize the need to cite/credit (which you definitely said as well, but in case other people are reading this too!). External music/etc *WITHOUT* citation is potentially grounds for disqualification.