Originally the rule I was taught was that you do not mix.
Mix away. I am doing a BOM from a LQS and they are mixed. Personally I like all batiks as a rule in pieced quilts or the background regular with appliqued batiks. Solid blacks with batiks (think modern Amish) are stunning in my opinion.
There is a difference and you may even need to reset your scant quarter inch. But the final product will be worth it.