Hardwood tend to be more porous than softwoods, so I use Minwax penetrating sealer, with or without stain, as the first coat, brushed on heavily. I top coat with gasket lacquer (it doesn't chip or crack if it's the right viscosity when it goes on) or Minwax polyurethane, brushed on. Gasket lacquer finished arrows are easier to pull from targets, especially if you shoot 3D. As to products rated for indoor or outdoor use, you don't have to worry about it unless you leave your arrows out in the weather. When it comes to wood, there's no such thing as waterproof, only different degrees of water resistance.
One advantage of the urethanes is that you can fletch very quickly with superglue.