Would you be able to share a model in which you are trying to do this, and/or the dimensions you are trying to add?
If those vertices are formed from the section view cut, then DimXpert won't be able to dimensions them directly since they aren't real model features.
Depending on the dimensions you are trying to add, there may be other ways than using the vertices. For example, the distance between the two right-most vertices could be added using the location dimensions to create two intersection planes, as shown below.
If you do want to use those vertices, then you could use reference geometry to put locate points and use DimXpert to dimensions between those points.
Alternatively, you could use a reference dimension (Choose the Smart Dimension thumbnail on the MBD toolbar > Reference Dimension) that would allow you to select the edges of the holes directly.