How necessary is it to marinade meat before making jerkies?
Marinating your meat makes it safer primarily by introducing it to salt, which kills bacteria. It is possible to make jerky safely without it, though you need to be careful.

You should use lean meat; fat is the most likely component in the meat to go bad.

It's also important to regulate the temperature closely and make sure hold the meat at temperature for long enough.

You can get some really really nasty bacteria if you don't cure meat correctly, so it's worth taking some time on it. Check out this guide on safely making jerky in a home dehydrator for more info.