I am aware that there isn't much desire to add mods to the official modpack and that players can always add JEI themselves, but I think that the mod could be a huge help to any new Pixelmon players. Pixelmon includes tons of items and crafting recipes. While most if not all the recipes are on the wiki, who wants to keep consulting it? Many players don't even know it exists. It might also help with figuring out how to obtain certain items (if Pokemon are identified as mobs), especially with how often drops change. Plus, BYG has plenty of items and crafting recipes but includes hardly any of them on its wiki, so this lets players new to that mod as well know what they can do with the items.
I'd say JEI is needed for a "minimal setup modpack" as much as BYG, Nature's Compass, Explorer's Compass, Fancy Menu, Konkrete, and JourneyMap. Perhaps even more than some of those.
Note: I've never tried using JEI with Pixelmon so I don't know if it is fully compatible, especially with how all mobs are replaced with Pokemon.