I have had a couple of fabrics that were HORRIBLE bleeders, even after pre-washing. And these were supposedly quilt shop quality fabrics (both RJR). So yes, always wash. Wash finished quilts in soap, not *detergent at least for the first few washings and use color catchers.
*Footnote: The main ingredient in detergent is soda ash, which helps dye to adhere to fabric. Soda ash will help any bleeding stay in your fabric.
A fix to dye bleeding is to "soak" the bleeding spots in Synthrapol or even dish soap and then wash in either of those two.
And definitely don't mix washed and unwashed fabrics in a quilt. Uneven shrinkage caused by doing this can lead to unpredictable results.