I’ll be using the D6374 motors in a very wet environment filled with water spray. I’ve heard motors brushless motors can withstand water, but any advice?
Well they’re open to the environment and they use shielded (not sealed) bearings so… not. Not even a little bit 
Based on this random website, https://www.axair-fans.co.uk/all-technical-information/ip-classification/, I’d guess it’s IP20 or IP21. I encourage you to try it and let us know 