Question: In the current draft of my book, the evil dictator whose body is encased in a silver alloy talks basically by allowing magic to move to seep into the silver shell, dispelling it and causing vibrations.

This voice sounds alien, imperial, and metallic. In order to represent this, I'm currently using a different font. (Specifically Kino MT.)

I do something similar with a group that constantly wear helmets that filter out certain wavelengths of sound, and use the 'Cracked' font.

They also sometimes speak in an imperial dialect which I represent with angle brackets.

Is this just going to reek of tacky amateurishness and such?

Answer: 
This is generally inadvisable (which is not to say that it is not done sometimes). The reason it is inadvisable is that every artform has its palette, its set of devices and conventions by which it tells its story. Mastering any art form is about learning how to tell the story within the confines of that palette. 

One of the limits of the prose palette is that is does not support sound effects. You can describe sounds with words, but you cannot reproduce them. 

One of the limits of the movie palette is that you cannot describe sounds, you can only make them. This means that all sounds in a movie are presented literally, and that it is impractical to present sounds that are injurious or painful to humans. (Movies have to fake this by using non-painful sounds and having the actors writhe dramatically -- something every third Star Trek episode seemed to indulge in.) Prose, by contrast can describe sound by metaphor, suggesting a far richer experience than a mere speaker can produce. 

So, you treat sound differently in prose and on video. 

What you are proposing is to represent sound through a font change. This is not part of the common palette of prose, so reader will not know what to make of it. This will tend to pull them out of the story world to ponder the meaning of your typography. But more importantly, there are other, richer, and more conventional ways to handle this in prose. 

You can describe the nature of the sound the first time it is heard, but if you really want to make a voice distinctive in prose, your best tools are distinct diction and distinct message (what is said, and the words chosen). 

Don't try to extend the palette of prose; try to become a master of the whole of the existing palette. It is more than adequate for any story you might wish to tell.
As noted above, "generally inadvisable" is on the mark.

However, if you consider your book to be more along the lines of entertainment, than along the lines of literature, you might do it. Really, the choice is yours.

Think of it this way: If you show up for a job interview, you dress in accordance with expectations. Same with books.

I write this not as a reviewer or publsher, but as someone who has browsed many books on the library shelves, always fiction, not necessarily in a genre that appeals to me. Although books with prominent decorative elements (including styled text) are uncommon, they are occasionally seen among recently-issued popular books, probably because those books are intended to appeal to the "soon to be a movie or TV show" market.