That would be the traditional solution, but they are always in the way on attractions and it's harder to find/retrieve items from them. Still that might be a better option. Has anyone ever used a Camel Pack?
"Whenever you find yourself on the side of the majority, it's time to pause and reflect."
I say use whatever you are comfortable with. Even if its a fanny pack.
I don't like to carry anything with me myself (like a back pack) because I don't want to have to deal with where to put it or what to do with it on rides. Hence... my use of cargo pants. But if you want to use the vest, by all means. Use it. Its Disneyland, not a fashion show. The point is to have fun and enjoy your visit. Just remember, June can be pretty warm, at least during the daytime so the vest might be a bit warn unless you just have a light t-shirt under it.
I have a similar vest, but I've never taken it to Disneyland. I want to use it, but it can't hold any clothing layers I may need throughout the day. So I just take a small backpack (and never have any trouble with it on rides).