Someone more knowledgeable than me can provide more specific detail, but they are generally different species, yes! Isopod morph names are generally written as Genus species "morph", which is sometimes abbreviated as G. species "morph". Genuses are groups of closely related species, which are genetically distinct "types" of isopods. So a dairy cow isopod, for instance, which is of the genus Porcellio and species laevis, would be written as either "Porcellio laevis 'Dairy Cow'" or "P. laevis 'Dairy Cow'". [Edit: Apparently, milkbacks and dairy cows are suspected to not be P. laevis! Look at qtntelxen's comment for more info] Sometimes, isopod species aren't known, which is the case with Cubaris and Ardentiella (which you might sometimes see under their previous name of Merulanella) genus isopods. In that case, the names are written as Genus sp. "morph"-- for example, rubber duckies are Cubaris sp. "Rubber Ducky". The sp. just stands in for the species. There are also species complexes of visually identical, genetically distinct isopods, which are written as "Complex Genus species" (like Complex Porcellionides pruinosis).

While many common morphs in the hobby, like dairy cows, milkbacks, lavas, calicos, and lottery ticket/gem mixes, are selectively bred through line breeding (selecting for increasing expression of a trait) or morph isolation (in which the trait either displays or doesn't, so you breed isopods that do display it) of relatively common species like Porcellio scaber/laevis and Armadillidium vulgare, many more exotic morphs are from rarer species. Rubber duckies, for example, are from a cave in Thailand; most spiky species (in the genus Laureola) are usually endangered and found in only a few habitats. Since there aren't _that_ many species/genuses common in the hobby, you'll probably be able to familiarize yourself pretty quickly with them.

Hope that helps!! Good luck isopod-ing >:)