The Collaborative International Dictionary of English v.0.48:

Idealogue \I*de"a*logue\, n. [Idea + -logue, as in theologue:
   cf. F. id['e]ologue.]
   One given to fanciful ideas or theories; a theorist; a
   spectator. [R.] --Mrs. Browning. Ideat

WordNet (r) 3.0 (2006):

idealogue
    n 1: someone who theorizes (especially in science or art) [syn:
         theorist, theoretician, theorizer, theoriser,
         idealogue]