Yes, evaporative coolers can be used indoors. Nevertheless, you need to figure out the humidity levels in your area first. If the humidity is lower than 60%, you can safely use your swamp cooler indoors.
However, if your humidity level is higher than that, or gets higher as the season changes, you cannot use the swamp cooler indoors. That’s because the air will get stuffy and swampy, making it difficult to breathe.