no, sand is not necessary at all to grow pods and macro algae. i do think a sand bed is good to have in a refugium though...even a shallow one.
you might want to do some research on deep sand beds. they have a controversial filtration aspect that is worth checking out.
the best place for a DSB is in the refugium. this way, if you needed to disconnect it from the main display for some reason, you could quite easily.