I am not sure if this is already a thing with project 4J, but I'd rather it be on legacy 4J. I do understand that the mod files all have their separate sections, but you could add a separate tab for the creative menu for finding these items, and either a separate tab, or just add the new recipes along the specific crafting 'genre'. I'd love to see this as a thing, especially in the creative menu. This kind of seems to work with already set recipes, for example; if I have 3 planks from the biomes o plenty mod, and 2 sticks, the crafting recipe will show up and still work in the crafting menu.

L4J is already compatible with mods, just enable the Display Vanilla Tabs option, and change the page, if you want to see all the recipes in the vanilla order. The same is valid for the Creative Interface, but you don't need to have this option enabled, just change the page (look at the control tooltips).