I've seen numerous rays that eat NLS, some grown out on it exclusively. One of the sponsors here on MFK (Shine Aquatics) has his entire group of black rays all eating NLS. His previous rays also ate NLS, almost exclusively, for years, up until he sold them. His gar would also eat the large floating NLS pellets, no problem. I watched an 8" leo cross smash back the 10mm pellets with ease, so there is no doubt in my mind that most rays can be trained to eat some of the less dense pellets, or wafers.
One of the mods here (Chaitika) had his larger p bass eating the 10mm NLS pellets like they were M&M's, but I believe that his aro later killed them.
Experience will vary depending on individual fish, and individual feed types offered in each tank. Typically palatability only becomes a problem with those that feed fresh/frozen as some fish will find those foods more palatable (no matter the overall nutrient content) and will hold out for those foods, and those foods only.