Should I inform the company that this recruiter is "cheating"?
This is really up to you, if this is against your ethical standards then by all means inform them about this situation.
In that case I would suggest you wait until you see the real questions you are given, to confirm if they are indeed the same ones as that recruiter gave you. Perhaps the recruiter was just giving you some clues on how the interview might go, and not necessarily the real questions to be used.
Again, you should think and decide if this is something you want to do (and given this new evidence, if this company is a place you want to work). The recruiter doing this probably means he is greatly interested in your profile, and wanted to make sure you got the job (not the best way to do it, though).
As far as we can tell, this could also be some sort of "test" to "measure" your ethical guidelines, so this seems to be a situation where you really have to be yourself and follow your ethical guidelines and your gut.
Edit: Seems that indeed the recruiter may have some ulterior motives for wanting to eagerly give you those questions and answers. Given this new light, you will still have to think this thoroughly (pondering your personal and ethical guidelines) to make up your mind to what you want now from this.
If you no longer wish to work there, but feel reluctant to tell about this situation, you can still go to the interview (and find out the truth so you can decide properly) and then politely decline any offer you may receive (for "personal reasons", "company culture", or the reason you prefer).
Anyways, it would be wise to start looking for other jobs elsewhere, just in case this doesn't work out well.