Running JER on a server forces clients to have it installed. While it makes sense to sync mod content, it should still not require the client to have the mod (and thus all of JEI, which is a massive RAM hog due to all the recipe indexing and whatnot) installed.

I don't think you need the mod server side in the first place.

well, JEI does have server-side components and it does sync some stuff. not sure if that extends to JEI plugins, but it's probably safer to just have a NetworkCheckHandler or something?