I asked a similar question (here and IRL/in real life) and was told
- if the spokes were not breaking, then it is worth a try, not an ideal thing but not a terrible idea
- it is best to sort the spokes into leading and trailing and use them in the same manner

I subsequently built a wheel re-using old spokes (that I forgot to sort) and it has been fine.

Then again, most spokes are not so expensive so there isn't a great reason to do this.