I think I see two types of fittings in the picture. Both types are used with EMT, so you probably have EMT there.
Is EMT allowed in a slab? Well, the general answer is 'yes,' since the article on EMT says so, and there are plenty of EMT fittings considered OK for use in concrete. However, we must still honor Article 110, which tells us the method chosen must be suitable for the application, that the method must be suitable for whatever mechanical or corrosive factors there are in the specific environment. Since concrete is porous, it is possible for there to be a slab that is exposed to solutions that make EMT unacceptable as a method.
An example of an 'unsuitable' concrete might be where the mix contains ocean beach sand. Such a concrete would have enough salt in it to seriously attack the rebar, let alone any EMT. While such concrete is no longer allowed for structural uses, I can see it being used in a simple slab, drive, or walkway.
Now, as for the fittings:
I see a die-cast zinc, or 'pot metal' type fitting. Such fittings are often listed for use in concrete.
I also see some 'crimp on' type fittings. Those fittings are not listed as 'concrete tight,' even though they are made of steel. The 'crimp' is a simple one-point indentation in the fitting.
As for your engineering spec: Specs often have a bias in favor of 'steel' fittings. This spec is based on simple snobbery, a belief that steel fittings are obviously, somehow, better than zinc fittings. My experiences do not support this bias.
In fact, steel fittings seem to be more dificult to properly tighten; it's harder to grip the more rounded 'nuts' with your Channellocks. In most environments, steel is more likely to corrode than zinc.
Sure, the cast fittings can be cracked, torn, and damaged more easily than steel, and zinc melts at a much lower temperature. However, if your pipe is moving that much you have some serious support issues, and wire insulation is destroyed long before zinc will melt.
Let's get back to this specific installation: I would say that IF the pipe is corroded to the point where there are holes in it, you should consider a different method. Perhaps PVC is a better choice. I would not worry about a little surface rust.
