I don't think it is going to be in your tank "naturally", so I would feed it (although I have heard of some very mature reef tanks that produce phytoplankton). I recommend DT's. I use it and it works well in my tank.
Right now the red flame scallop is the only invert I have that needs phytoplankton I think. I also have a linka starfish and the above mentioned shrimp and crabs. I am preparing to buy a pink tip haitian anenome and I bought Coralife Ivertebrate Target Food in preparation. Is that good food? Will it feed the scallop too?