I've not only kept and grew a H. crispa in 100gal reef under 6x 48" NO 32watt t8 zoo-med bulbs but it regained all lost zooxanthellae of it's bleached condition when new. I've successfully kept S. haddoni (3years) and E. quadricolor (4years), under the above standard output fluorescent bulbs. All of the above were traded back to the lfs's when i lost interest or wanted to try another species.
The watts/gal rule doesn't work. the above was on a 100gal aquarium. I now keep sebae's (3years), and a lta (new), under 4x 48" HO 54watt t5's over the same 100gal 72"x18"x18" reef. That's 216watts on a 100gal = 2.16watts/gallon, or you could say 216watts over 67gal (48") = 3.2watts/gallon.
I'd say he can keep anything but the following exceptions; H. magnifica and S. gigantea require higher light energy, also the 50gal breeder is the wrong dimensions for H. magnifica. S. mertensii is another because it'll grow much too large.
Keep in mind that well you have enough light for S. haddoni, it would dominate and out grow a 50gal breeder. H. crispa would also eventually be a little cramped too.