Short answer: No. Buy an Agent instead.
Longer answer: A GM may allow a spirit to default on a skill it doesn't have. A very generous GM, in the case of a Spirit helping on a Matrix task. Still, so long as the decker were in AR he can still perceive that Spirit attempting to assist in a teamwork test. A more practical way for a spirit to assist would be to simply play watchdog over a limp body while the Decker is in VR. In the specific case of a Spirit of Man, if you know the Improved Logic, Willpower, and/or Intuition spells the Spirit can cast and sustain them on the Decker.