Can I reseal a black Marley floor? If so, will this prevent the dye from ending up on the dancer’s clothing and shoes?

There is no dye in Marley floors. Color pellets are added in the manufacturing process and are part of the floor material. What is getting on the dancer’s clothes is most likely aluminum compound, tap residue. Shoe and clothing dye get embedded in the flooring and do not transfer. You can put a finish on the floor such as FloorShield II that will help prevent the tap shoes from disintegrating. Steel and aluminum taps will eliminate the problem. See the maintenance guide at stagestep.com to learn how to clean up tap shoe residue.