Is it possible to hack somebody's snapchat account?

There are many ways to do that.
Although, Snapchat is safe to use, you can always access its data.
For example, for any reason you are able to access someone's cellphone, you put a keylogger on it and any other spyware to get the photos, media, etc...
Snap itself is safe, but if you can get into the cellphone you can track and log all the user's inputs, data into a server.