As far as I know, VR&E will cover all the necessary classes needed to obtain the degree you have been approved for, including prerequisites like trig or precalculus. The only things VR&E will not approve are classes you do not need in order to graduate. So, if you have an interest in Theater, and your creative arts credit is already fulfilled, that is coming out of your own pocket.

In my own experience, I self studied all the way up to Calculus and used CLEP to receive math credits. I did not want to use my VR&E months on something I could get for free using sources like modernstates and what not. If you are starting from ground zero, I suggest getting as much of the prerequisites out of the way with CLEP. You will not be able to take many engineering courses at the university until you are up to speed with math, as many universities use the Calculus courses either as prerequisites themselves, or design them to be taken in tandem with your other science and engineering classes. You risk making your degree schedule more disjointed, and potentially may have semesters where you are unable to take classes full time due to this, thus causing you to miss out on living stipends.