Well yes. Engineering, well the theory for a lot of engineering courses will involve a lot (I really mean a lot) of differential equations and such. Complex numbers can be used to simplify a lot of problems. For example, in electrical engineering they can simplify capacitor circuits and such, instead of doing 2 or 3 pages of working using only the real plane, you can take shortcuts and do the problem in a few lines, and a lot quicker. The same goes for solving certain differential equations. Some of the abstract stuff we learnt in Linear Algebra last sem (I'm talking uni lin alg, it's not as simple as straight lines, it's pretty bloody confusing actually), can actually simplify solving a few things a hell of a lot quicker and with ease. At first it seems useless, but later on you see it's uses.
Euler's approximation (and better variants of higher orders, i.e. 5th and 6th order approximations) are very useful for solving differential equations that don't have exact solutions, except later on in uni you don't really use it, rather you need to know how to program it, then get the computer to do 10,000 iterations with a small time step in a couple of seconds. (Although for an exam we had to do 15 iterations of a fairly annoying equation on a damn scientific calculator).
Most of what I'm talking about is more applications from what you lead onto doing at uni later on, not exactly what you cover in VCE. To be fair though, the content in VCE is pretty basic, but you need these basics to be able to do anything later.
Although, with all of this being said, this covers the theory needed for eng, I'm not out in the field yet and such, but nowdays a lot of the calculations aren't done by hand, there are better ways of doing it, or even approximating it. Computers can do things a lot quicker than we do. But, you still need to know and understand how the theory all works, otherwise when the computer spits out something that's wrong, how are you going to know that its looks odd, instead of blindly using it and letting something break. You don't want to be blindy using something without understanding how it works, you'll need the understanding to work out what to do if you do need to change an input, which way the output will go, and whether that is what you want it to do. Sometimes you will need to know the theory to be able to program the computer to be able to do and spit out what you want it to do. If you don't understand how this works, then you're not going to get anywhere. Although, this could be biased more because I'm in aero, talking to a postgrad student who did electrical eng, 'apparently' electrical and chem do more by hand, and aero do a lot with computers and approximations, I don't know how accurate that is though.
So yes, for engineering, of course you'll need them, different disciplines of engineering will need differing amounts, but it just depends how it's all applied. If you know your stuff you can do a quick approximation to determine if something should be tried or not, before going to computing power to do it.
EDIT: Take this with a grain of salt though, as I'm not working as an engineer yet, merely a student. Most of the above is just what we've heard from lecturers, tutors, postgrads and such. So if there is anything that's not entirely correct, then pick me up on it.
Also my post seems all over the place. I tried to organise it a bit better, but think I just made it worse.