What will happen if you bake seized chocolate into a batter?
Using seized chocolate in a cake recipe is going to impact the texture of the cake. The chocolate can't distribute properly throughout the batter, and it won't incorporate cleanly during baking, so you will end up, at best, with inconsistent flavor (and possibly color, depending on other ingredients in the recipe) throughout the cake.

Using chocolate that seized because of contact with water is not as likely to produce a grainy texture and shouldn't affect the overall flavor (except as noted above). Overheated chocolate, however, will affect the flavor and the texture, giving the cake a slightly burned taste and a grainy/gritty texture.

In general, you're better off just starting over with the chocolate than trying to use it after it has seized.