Not only are creators not legally allowed to use fan-suggestions, but you have to realized they get them all the freaking time and it's incredibly presumptuous to think that your ideas are worth their consideration. They're professionals, their creations are their babies, they already know what sort of characters and concepts they want. They don't need anybody e-mailing them with "I think your show could use THIS and THIS and THIS!"
It's also incredibly silly to suggest voice actors. Creators don't get their pick of voice actors. They have ideas of who they might want, sure, especially if they've worked with those actors in the past, but they have to be available, willing, contracted and paid. You can't just use whoever you want or tell people who to use.