Well if it helps contextualize this a bit, take a listen to some of the past competitions on here (like 2010 & 2011), and check out how they integrated the sources. Also, while not strictly called for, a good rule of thumb on handling the sources would be to pretend you're writing it for OCR - that is, make sure either of the sources are recognizeable for at least 50% of the track (either in the background or front & center). In 2011, for example, I did a funky arrangement where I pulled from plenty of alternative sources (including Schala, for shits and giggles) - but I made sure the sources I needed to include were there for at least 50% of the track. I'm certain if you want to do some more original writing you'd be alright as long as there's about half of your arrangement where people can recognize the sources somewhere.
Aside from that, go nuts - whether the source is in the background over something more original or if the sources are more front and center, as long as they're there. Just realize that this is being voted on by regular people and not necessarily judges, for better or worse, so I suggest not being TOO subtle with your sources. If people feel like you're not really arranging the sources and instead going on your own rail that could impact the vote (even if you can prove that you're subtly using the sources). Of course, time stamping in here wouldn't hurt your chances if you feel it's pretty subtle, so hey.
Hope that helps a bit!