Confusing ain't it? Took me a long time but I feel like I am getting a grasp on all the malts out there.
Here is my take. Every maltster likes to give their own malt its own name to differentiate from all the others out there of a similar type. Weyerman is particularly fond of this, even trademarking their malt names! The malts all are different to some degree in that each maltster kilns them in their own way, uses different source barley, etc.
That said they are of a similar type and can be substituted but will have their own individual character. Whether it is a strong or subtle difference depends on the overall useage and recipe.
Melanoidin is supposed to mimic the effect of decoction mashing as I understand it. Adding melanoidins you would get in that process. Aromatic is supposed to add malty aroma and to some extent flavor/mouthfeel. Which arguably is the character melanoidins, products of maillaird reactions.
So, anyway my rule of thumb is look at what the maltster is claiming their malt offers and then at the root of it you can tell what type of malt it actually is. A crystal, roasted, base, toasted, etc...