I don’t know enough about reef lobsters to give you a good answer. . . But
Unless you are setting up the tank specifically for filter feeders, I would skip the scallop. The consensus is that in captivity they die quickly due to starvation (I didn’t do enough research before I bought mine (fish store said they were easy no problem)) and it lasted about 6 months (and I was target feeding it at times). I’m sure they can be kept in certain set ups, and maybe some people have better luck, but again the consensus is they die quickly in captivity.
Scallops can swim (clams can’t? at least as far as I know) but mine only ever hunkered down when disturbed, never really ran away.
I guess it would depend on how strong the lobsters claws are, how determined it is, and how hungry it is. . .