Electronic supplementary materials for scientific journals
I cannot tell for Springer or Elsevier, but a couple of years ago I published a paper in an IOP journal which contained a table with several diagrams.

I submitted the diagrams separately and included them in the table's cells with \includegraphics, as I did it preparing the manuscript. It worked.

Each journal has its own idiosyncrasies when it comes to LaTeX practices. When the guidelines do not provide enough information, my strategy is to first try submitting the files as they are, following my workflow, and if it doesn't work I resort to other solutions.