No, a domain-consistent all-different propagator such as the one desccribed in [1] is sufficient to determine a valuation domain for a Sudoku puzzle without any search.

Of course that does not hold in general, but in the special case of Sudokus and problem modelling by a domain-consistent all-different propagator, no search is required for a solution.

[1] A filtering algorithm for constraints of difference in CSPs, J-C. Régin, 1994