Most time, if washed thoroughly (no scented fabric softener... and if used, rinsed very, very well) and dried away from the possible addition, the allergens are washed away. Acrylic, being the fiber of choice for a good number of types of projects, happens to wash and dry well... which is one reason for the use in the first place.

You can always ask ahead of project start to be sure - letting them know that the wash and bag/box will be done away from home/cats. Good luck!