I've never seen a ribbon (or prize money) awarded specifically for the fabric used in the quilt. I'm just saying that it is a nice courteous gesture to let your quilter know if her work helped you win a ribbon, especially if the ribbon was for quilting, whether it was by hand or machine.
If I were to get a judge's comment back with compliments about the fabric, especially hand-dyes, I would also let the dyer know about it.
I like to give credit where credit is due.
For instance, the current (Fall 2011) issue of ON TRACK magazine (for machine quilters) has beautiful photos on the cover of a TQS BOM made and quilted by Marlene Hiltner. The article does state that it is a Sue Garman design, but I would like to have seen TQS mentioned also.