There is a good deal of misinformation on the Internet regarding the backup/archival copy exception. It is not a "second copy" rule and is often mistakenly cited for the proposition that if you have one lawful copy of a copyrighted work, you are entitled to have a second copy of the copyrighted work even if that second copy is an infringing copy. The backup/archival copy exception is a very narrow limitation relating to a copy being made by the rightful owner of an authentic game to ensure he or she has one in the event of damage or destruction of the authentic. Therefore, whether you have an authentic game or not, or whether you have possession of a Nintendo ROM for a limited amount of time, i.e. 24 hours, it is illegal to download and play a Nintendo ROM from the Internet.
Essentially, unless the person made the backup themselves, it's an illegal ROM. I know this isn't the time nor the place to discuss the legality of ROMs, but I really don't think you should be telling anyone it's legal either.
Other than that, though, interesting what you've done so far. Is it just the first generation that's going to be available, or will you incorporate the other generations into Kanto in addition?