Most powders are very hard to positively identify except for a few like Red Dot, Geen Dot, etc. that use specific markers. Best to dump the powders and not take any chances.
Unless the bullets have been deformed from pulling there is no reason why they can't be reused, especially if they are just for plinking.
Cases can obviously be reused unless they have splits. You should resize them, however.
If you are careful depriming the cases the primers can also be reused. Just ease them out during the resizing process (don't yank hard on the press handle). I have deprimed hundreds of buggered up reloads and reused the primers and never had one detonate yet. They won't fit as tightly in the primer pocket as virgin primers but will still work fine.
in short the only part of salvaged reloads I would hesitate to use is the powder if you don't know for sure what it is.