This has been a bit of an issue that has been in the back of my head for a while, but this is regarding to how Fire Emblem characters are.
Presuming what we've been shown will be in the final product, there would have to liberties to make sure Fire Emblem characters feel just as versatile as the Shin Megami Tensei side. You might not think of it much, but there are a surprising amount of Lords that do function very similar to each other, which not taken into consideration could really lead to a dull roster of characters. It is in theory a very possible thing to do however, as shown to an extent with Fire Emblem: Awakening where the varies past characters were given more distinctive characteristics. I speculate that when this crossover comes out sometime in the future, liberties will be made for the sake of a much more versatile roster. However, what those liberties are is another question entirely.