The Collaborative International Dictionary of English v.0.48:

Vouchee \Vouch*ee"\, n. (Law)
   The person who is vouched, or called into court to support or
   make good his warranty of title in the process of common
   recovery. --Blackstone.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vouchee
    n 1: (law) a person called into court to defend a title

Bouvier's Law Dictionary, Revised 6th Ed (1856):

VOUCHEE. In common recoveries, the person who is called to warrant or defend
the title, is called the vouchee. 2 Bouv. Inst. n. 2093.