You can't use modded furnaces to cook the unfired procelain.

You CAN, however, use them to smelt unfired porcelain barrels

Alright, I've moved registering those recipes from postInit to the oredictionary event, so unless a mod is registering their oredictionary super late it should appear in other mod's furnaces.

Which modded furnaces are giving you issues? I have seen several packs with modded furnaces that work fine

The recipe only shows a vanilla furnace in JEI.(this is part of the problem)

It does not work in a thermal expansion redstone furnace which was the first one I tried, then looked up the recipe.
It does work in a mek, futurepack and Industrial Forgoing (I had not tried them because the recipe didn't show)

Recipes moved to event in 1.3.4