A lot of singers get hung up on the concept of "Classical" training. They think if they are trained "Classically" they'll sound like an opera singer trying to do rock or jazz! That is not the case!

What's important in all styles of singing, is the function of the vocal cords. The cords are controlled by two sets of muscle systems. Like any set of muscle systems in the body, there are specific exercises that will make them grow and get stronger. Classical training means that the exercises employed by the singer, as prescribed by the teacher, are done to make the voice stronger, with proper function. The style of singing is up to the singer and an experienced teacher will work with the singer in whatever genre that singer chooses, making sure that the voice is functioning properly. 

So don't get spooked by the term "Classical". There are specific ways to train the cords and those ways have been around for hundreds of years, because they work! They work for every style of singing!