Judging totally by wowhead comments, it looks like it's a flat 50% chance to drop extra cloth. That chance doesn't go up with additional tailors and what does drop is first come first serve among the tailors in the group. So it doesn't seem there is any bonus to leveling more tailors.

As far as the Warrior, I don't think he'll be able to see the cloth. I'm fairly certain you need 325 tailoring to see extra Frostweave and 400 for Embersilk.