If you're felting the project then it is possible they will felt differently. I recently made felted slippers and I originally chose two different 100% wool yarns for sole and upper. I made a swatch first and felted it to see what the results would be. One of the yarns didn't felt near as much or as quickly which made them unacceptable for the slippers and I had to choose a different yarn.
So... Consider what you're making and swatch it first. Wash and block or felt it as the project will be and you can tell if it'll work for your project.