well the main function of a sand sifter is to sift sand. hence the name
It seems logical that a few might munch on life in the bed, but hey, it's a give and take relationship isn't it? Just so long as you don't throw in too many things that strip the bed (what those include, I don't know) of life, I think things will turn out anywhere from okay to better than before. At least you won't get the black-anoxic-toxic-and-generally-just-plain-icky sand that unstirred DSBs are known for.
as for suggestions for a reef sifter, i hear good things about various gobies. sand sifting stars do a good job. cucumbers are up there too, but Id go for a non toxic one.