Hi! Yes it can be used for commercial games:
LICENSE:
You may use these assets in personal or commercial projects. You may modify these assets to suit your needs. You can NOT re-distribute the file, no matter how much you modify it you can use it but not share or re-sell it.
As for RPG Maker, I'm not familiar with RPG Maker that much. I guess that if you can import tilesets, you should be good.
Thx!