Is it allowed to bring in voice amplifiers with a microphone in Disney parks so you won’t have to yell across the way to see characters?

No, that isn't allowed.

I believe those would likely fall into the category of "megaphones" or "artificial noise makers," which are not allowed on Disney property.

This would not allow you to see or interact with the characters any easier.  Screaming at the characters through a microphone won't get a response from them. You have to wait in a line to meet them and take a photo with them. 

Obviously not!  And how would yelling help you to see characters?

No it’s not allowed, and it would be taken away, seriously you are going to do that to characters?

i would call the parks and ask them