Srila Prabhupada explains in Caitanya Caritamrita that one may even accept diksa from authorized disciplic succession, but still it can be found that he will preach Mayavada philosophy. So it is not the diksa itself which establishes the real connection to the sampradaya, it is the siksa, or strict following of the instructions. Although both siksa and diksa are required for one to be connected to the authorized sampradaya, still the primary connection is through the siksa.
Riga SB 1 1 22