Board Thread:Naruto Discussions/@comment-30168130-20161009021213/@comment-1512913-20161009124032

Curse Mark users have never been stated or shown to absorb natural energy though, through their curse marks or otherwise. Curse Mark was only said to contain a modified enzyme extracted from Jugo's bodily fluids which is responsible for Sage Transformation, but besides Sage Transformation, there hasn't been any implication that Curse Marks also possess the passive energy absorption aspect of Jugo's kekkei genkai.

While it sounds sensible what you say and I would actually agree with it, problem is, Orochimaru himself absorbed Senjutsu chakra from Kabuto suggesting that he himself handles it, instead of him just putting his ordinary chakra into the Curse Marks, which then absorb natural energy on their own to turn said chakra into Senjutsu.