It is perfectly legal to download the RTP resources without paying for RMVX Ace. Otherwise, only people who owned RMVX Ace could ever play games made with RMVX Ace that used RTP resources. When you download the RTP, you are given a licence to play any game created with RMVX Ace. The EULA says that you can only use the Ace RTP in another RM if you own both RMVX Ace and the other RM, though for some reason that's not a numbered provision. Either way, it is in the EULA and it doesn't technically matter if it is commercial or non-commercial.
That said, breaking the EULA is a breach of contract and copyright infringement. So it is illegal in the sense that the law will enforce a claim for damages by the copyright holder, but not in the criminal sense. Copyright infringement can attract criminal liability, but I think that is only true if you are seeking to profit, so then it would matter if it is a commercial or non-commercial project.