The manual only talks about vane flex direction for the Jabsco pump. The exploded view of the pump in the manual (to show vane flex direction) would indicate the impellor would turn CLOCKWISE in the pump housing if you are LOOKING AT THE REAR OF THE PUMP with the cover off. On the other brand of pump, it simply says put in the impellor and put the cover on. This would imply the vanes are self-setting, but it simply does not address this.
For what it is worth, the manual states you should not lube the impellor with a petroleum product. Don't know if this includes Vaseline or not, which is what I always used to use. I use straight dish washing detergent on this one, and it seems to work fine as a lubricant. Vegetable oil should also work.
If this is not clear let me know and I will try to send you that section of the manual.