Using various versions of agricraft and Biomes o Plenty up to the most recent of each, it seems that greenhouses do not spawn in BoP world types. I am also Using Witchery, Tinker's Construct, Flaxbeard's steam mod and Thaumcraft, all of which add custom village generation which does appear to spawn correctly.

I believe it's simply due to the fact that the footprint of the building is too large.

Drats! That makes me sad. The greenhouse pic's I've seen thus far look very nice. Thank you for the quick response.

I'm not sure, i'll have to add in some debug info to see when it is called to generate and why it can't