Among the "Evangelical Catholics" (notably Yeago and Root) it has become fashionable to claim that the theology of the cross is not central to Luther's thinking. Root in particular has noted that the term only appears 3 times in his corpus. This is rather irrelevant though. A conceptuality obviously be present without a specific term being used. "Thesis-Antithesis-Synthesis" is never used in Hegel, but the conception is clearly there.
This brings us to the Genesis commentary. One could of course claim that theologia crucis was only a part of the early Luther's theology. It is also correct to attack certain existentializing tendencies in 20th century Luther studies. Also, the partial form it takes in the Heidelberg Disputation, one could argue is still pre-reformational. I would actually tend to agree with that, in that I would agree with Brecht and Green, and some other people that the Reformation breakthrough occurred in about 1519. I would also tend to agree with Kolb and Arand that a better matrix to understand Luther's thought is two kinds of righeousness or Bayer that the "orders of creation" is central (actually I think a combination of these approaches is good). Certainly the Genesis commentary would bear these approaches out.
Nevertheless, I don't know how one can read the Genesis commentary and think that the theology of the cross also not a valid interpretive matrix. Luther consistently notes how God appears hidden under weakness and how human being always hate weakness and are attracted to big and flashy signs of power. Humans are passive, God is active. God speaks to us under weakness- sinful humans desire power and vision. It's on every page. It's very hard to miss.
In fact, I think it depends on how you construe what the theology of the cross is. For example, I would construe it as an approach to theology that plays knowledge as vision against knowledge as hearing. It would also more generally be an approach to theology that plays divine action which we, (to use Bayer phrase) "suffer" off of an approach to theology where we are active and "participate" in divine knowledge and the process of redemption. If that's the case, then there can no marginalizing these themes in Luther's thought.