Can I connect two buildings with a greenhouse?

Yes, we call this a breezeway.

Yes, this would be considered a greenhouse breezeway without gable ends. We would treat this sort of project as gable-attached to the building on both sides. This is often a great use of space for an unused area between two buildings. 

When speaking with your greenhouse expert, they will be able to assist you in creating the project that fits your needs.  Often sending us a photo is a great place to start!