Most research paper agrees that the upper limit of cell tolerance to DMSO presence in their cell culture media is about 1% final DMSO (this might vary with the cells and media).

In the case of the Nucleofection, the DMSO will likely be transfected (at least partially) into the cells causing more harm to the cells than just being present in the culture medium. However, there would be the possibility of diluting the DMSO presence after Nucleofection by adding enough medium to fall largely below the 1% DMSO final in the culture medium.

DMSO concentration should not exceed 3% in the final Nucleofection volume.