The legal perspective:
No, you cannot legally redistribute someone else's copyrighted work.
This is international law. It is not debatable. It is not made okay by giving credit. It does not become okay by giving it away for free. By copying someone else's copyrighted work, you are violating their copyright -- literally, their exclusive right to make copies. (Yes, there are some circumstances in which you can defend the practice via the doctrine of Fair Use, but this does not cover your situation.)
You cannot legally redistribute someone else's copyrighted work.
An employer's perspective:
Speaking as someone who is occasionally involved in hiring programmers in the games industry, I would never consider hiring someone who submitted a demo containing illegally copied materials. Hell, if the graphics weren't yours, I'd start wondering whether the code was really yours, and whether you didn't just find some code somewhere and re-purpose it.
Hiring a programmer who behaves in this manner would be a massive risk for the company. Imagine the scandal for the company if you did such a thing while working for us, and we didn't notice but you got caught by the media. No, I will not take the chance of hiring someone who has a known history of acting in this way. The risks are too high for me, as a potential employer.