No — onions damage dogs' red blood cells.
Onions (raw, cooked, or powdered) contain compounds that destroy dogs' red blood cells, causing anemia. Damage builds up over repeated exposure, so even small regular amounts are dangerous. Garlic, leeks, and chives are in the same family and carry the same risk.
If your dog already ate this, don't wait for symptoms — call your vet now, or the ASPCA Poison Control line at (888) 426-4435. Note what and how much was eaten.
Get the printable list of the 30 most dangerous foods for dogs.