Couple of things,
1) Reptile forum
Most of us know SFA about mammals.
2) Head and shoulders can be hard on people scalp, don't even wanna know what it'll do to a dog. Talk to your vet about the dog's skin condition and use the appropriate treatment after talking to your vet.
So no, it's probably not OK to use on your dog and it's entirely possible that it's not dandruff at all. Talk to a vet.
and just in case it wasn't clear yet, talk to a vet