There are minus and pluses in both cases. Bd6 is the approach in the modern stonewall variation cause develops the bishop in a more active square but also give the right white to trade this piece with Bf4 and that is strategically bad for the continuation since white will try to use blacks weakness on the dark squares.
Even in the classical Dutch it's sensible to begin with the bishop on e7 and according white's game to develop this piece further. Sometimes it's preferable to play direct Bb4 and pin the c3 knight in order to avoid e4 and finally trade it quickly for the knight. For what it matters there are theories and examples if you run in books and databases.
Why is 4. Be7 recommended in the Dutch Defense?
What is purpose behind this move?
Would 4. Bd6 be a legit alternative?
Why or why not?