I...
I don't see the harm in it. As for it "not fitting the theme", considering we have arcane and dwarven engineering (Rune cannons, steampowered naval vessels, extremely-difficult-to-create LIGHTSABERS), I don't see how it'd ruin the theme already established. We don't have to go full steampunk, and simple firearms don't qualify as that. It's Renaissance weaponry at the most, and that doesn't ruin the high fantasy feel of LotC.