Do I need isolation footers for my components if I'm already using an isolation rack?

Here is an easy exercise, to answer your question.
Gather household items: rubber doorstops, protective furniture leg discs, pencil erasers, pill bottles, wooden cubes, different
kinds of tape.

Place them under and on top of: electronics, cables, 
ends of power cords, speaker cabinets.  You can even use them in some combinations, together.

Some will improve the sound, some will make it worse.
The piece that improves what you hear in one application, might not work in a different one.

This is a harmless, low cost way to experiment with tuning your system.  The higher the quality of your setup, the easier it will be
to hear changes.

At some point you may want to make an investment in
products designed for these applications.

Make it fun.