No it will not drain and the bark will rot. But you could put down weed suppressant membrane than a thick layer of bark. I have done this and it works well, but you do need to dig out and clear the weeds first or some will come through the membrane.

Depends on how deep the bark will be. Over 2 inches and the weeds will struggle to germinate and grow. If they do then they will be straggly and easy to pull out. Personally I would weed the area first then rake over the area then put down the bark. I did use weed suppressor stuff under bark where my kids swing and play area is - weeds still grow on top of it and through it unless the bark is deep enough but as I said they pull out easily enough.

Snap with Drc!

id use broken slate as eventualy the bark will rot down .