Ahh, so if I'm understanding correctly, you're trying to apply a morph that works on what is usually the torso mesh in Daz? If that's the case then that morph will need to be applied to the main character mesh and not the genitalia mesh. Once you have it applied to the body mesh:
- Select the genital mesh, then shift and select the body mesh so that it's the active selection (highlighted)
- Under the Morphs section of the Daz Setup menu look for the Transfer Shapekeys option
- Hit that, select the morph in question and hit okay
That will transfer the shapekey vertex data from the body to the genitals so that when you change the morph under the Daz Runtime morph menu, they'll both deform uniformly. If that works for the genital mesh morph then it might work for the others that are being problematic.