Replace the soft word "warez" in your description above with "stolen property" and it might help make the issue less morally ambiguous. It's theft, plain and simple.

Why would you want to work for them? If they believe this is ok, it's only a matter of time before you're screwed over too. If it is an oversight on their part, you breaching the subject is much better than them eventually realizing they have an employee who is fine with dishonest business practices.

You should be able to broach the subject in a professional way; if you're dismissed because of it you have grounds for a lawsuit.

Incidentally Microsoft (and probably other companies) has a great program called BizSpark to help startups get over initially prohibitive software costs. You might want to bring this up to the founders as a solution for them to make sure they're legal.