That's fine! I'm personally okay with downloading one but not everyone might be so it might affect how many people are able to play and rate your game! 

There are web-native emulators for numerous retro consoles, including the NES. :) Maybe you can make your NES ROM playable on Itch by following this guide: https://www.matthughson.com/2020/07/17/nesdev-embedding-an-emulator-on-itch-io/