I think it would be fine. Nylon won't shrink whereas cotton fabric often does shrink, but even so it should not be a problem for quilts or baby clothes. For baby clothes, I would probably pre-shrink the cotton fabric before cutting and sewing. I do not normally pre-shrink fabrics for quilts and probably would still not bother to do that even if using nylon rick rack on a quilt.
If you are at all unsure, make a test swatch of fabric and rick rack and wash to see how it turns out. Do the same with a quilt test sandwich. Sometimes a test swatch can save you a lot or worry and/or a lot of disappointment.