Board Thread:Theories and Speculation/@comment-45444155-20200728155230/@comment-3279282-20200801130313

The 4th db states that Kabuto learned Sage Mode at the Ryuchido. Jugo says that in his village, Kabuto's mode is called Sage Transformation and that Orochimaru undid Kabuto's Sage Transformation.

So yes, Sage Transformation is without a doubt a form of Sage Mode.