ChatGPT really isn't that good at creating code. But it can maybe help you create something very simple. I would be surprised if it's not allowed. Googling should always be allowed on any jam, and no one's stopping you from using a youtube tutorial to make your game. However if it looks like something someone else made 100 times before already, maybe it won't get that good ratings.

Idea: Make a game using a youtube tutorial and then attempt to learn to create your own graphics/textures for the game?

Choose a relatively recent tutorial, as some features in Unity have changed too much over the past years and 6 year old tutorials won't maybe work anymore.

Regarding Unity tutorials on YouTube for beginners, i would recommend to check Brackeys's channel. It's a good starting point to get used with Unity in general in my opinion, even it's not that recent it's still relevant.

However, even if it's allowed, using ChatGPT may be not that good. I think you won't learn a lot doing this but it's completely up to you. Instead, try to find answers on Google first (by the way ChatGPT often gives bad or not working codes). There are a lot of trustfully forums like Stack Overflow that will answer most of your questions, but most importantly that will explain these answers.