Rental income of an office space (a sublease) by a partnership (LLC with member-managers) without any of the partners or employees providing 'substantial' services to the sublessor is not self-employment income.  If I am right, I will have saved the partners significant taxes.

This partnership provides consulting services in a specialized field. 

It seems that the question of SE income turns on the question of whether the activity is a TOB. Since consulting is the primary activity, this sublease is not a TOB.

IRC 1401 is an area of the law that I should spend more time learning.

From CCH:

Rentals from Real Estate. Rents from real estate—as well as rents from personal property leased with the real estate—received by an individual who holds the property for investment are generally not included in net earnings from self-employment income. For example, rents from the operation of a mobile home park are not included in net earnings from self-employment. However, rents paid for services that are for the convenience of the tenants as opposed to services required to maintain the space rented to tenants in condition for occupancy are included in net earnings from self-employment if the services are substantial enough so that payment for them are clearly a material part of the rents paid by the tenants.