It actually does appear in the Rodelheim, but it isn't part of Nusach Ashkenaz.
There is no problem to say Yigdal or any song of Shevach before Davening, (it isn't said in a way of learning - Derech Limud, so there is no problem saying it before Bircos Hatorah).
[There were problems with other Kabbalistic techinos written in the recent generations, for different reasons].
Michael
FRBSH