Is there a way to tell NEI or similar mods to ignore and not list certain blocks?

 

I would not want to clutter up the list with individually-useless things like ghost/gag blocks and the like.

 

I assume for regular creative I can just not specify which creative tab the block resides in but I assume mods like NEI use other means?

Or am I completely wrong and NEI also only references creative tab blocks/items?

Use the mod's API. Specifically for NEI, use its API:

https://bitbucket.org/ChickenBones/notenoughitems/src/8986f98aef1e38bc09f9ea5c5ebed4af6aa05d27/codechicken/nei/api/?at=default

 

You want to use API#hideItem(int id)

Thanks, I'll look into that.