I would not prewash. However, I would use Synthrapol to wash the quilt the first time. Synthrapol allows any unset dye particles to be suspended in water and rinsed away so they do not settle in other fabric. This is the most reliable method of making sure nothing gets stained from bleeding fabric.
Also, you can do some tests on small pieces of fabric to assure yourself there will be no massive bleeds. Take a damp piece of white cotton fabric and rub it on each fabric. No dye should transfer. You can also snip off about a square inch of fabric and immerse it in a clear glass of water. Leave for a few hours. If the water is clear, fabric won't bleed excessively.
If one of the fabrics bleeds a lot during the testing process, you will have to be super careful about the first few washings -- use Synthrapol, remove the damp quilt immediately to dry, and keep using Synthrapol until wash water isn't colored.
Salt and vinegar were traditional methods of setting dyes in fabric. However, each works primarily with a subset of organic dyes. Almost all fabric dyes these days are chemical dyes, so salt and vinegar often have no effect. The purpose of using salt and vinegar, anyway, is to set dye in fabric. If you were to use these, you would want to use them on the fabric before making a quilt. Retayne does the same thing but is more reliable on chemical dyes. You would not want to use these on a quilt because they are designed to set dyes, including bleeds. You do not want to set a bleed into another fabric.