If the problem does not look like a break (and mom stepping on and breaking a tail is not uncommon in the breed) then I'd not suggest the kink would change.
If the vertebra were not formed right and caused a kink from birth on its unlikely the bone formation would change as the dog growsh.
It may become less obvious as muscle and coat cover the tail.
This is considered a fault in the conformation of the dog according to breed standards in several countries including the US
http://www.akc.org/breeds/great_dane/index.cfm
http://ultramarine.org.ua/pages/standard_eng.php
So these would not be dogs to show or breed.
Hope this helps you!
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