It won't make a difference what direction the vanes are, as long as none are touching the riser upon release.

The whisker biscuit is a great hunting rest. If you have any trouble with vanes, then just get the right type and glue them properly and they will hold up great. A refletching jig can come in handy, not just for the whisker biscuit, but for the hundred reasons you'll end up having to refletch your arrows anyway.