Can I use cake flour in place of all purpose flour in brownie recipes?

No. You will not get a brownie texture if you use cake flour. If you're okay with chocolate cake, then go ahead.

Yes, they will probably turn out fluffier. It should be noted you will need to increase the amount of flour for every cup of all-purpose flour the recipe calls for add 2 more Tablespoons of cake flour.
1 C. all-purpose flour = 1 C. + 2 T. cake flour