Rocks'n'Diamonds

Is the name of the constant (#define) always "EL_" + the element's token name?

I see that it is this for most elements, but is it like this for them ALL?

Yes, it is.

There are some subtle exceptions, though: Elements like "dynamite.active" ("EL_DYNAMITE_ACTIVE"), which are a combination of an element name ("dynamite") and an element action ("active"), but which also exist as a true element that can exist in a level file.