"His work(s) in research and teaching [have/has] been"
Of the three you list:
His work in research and teaching has been ...
is the best formulation.
Perhaps:
His work and teaching have been ...
Work in academic context functions as a group noun that reflects all of his works as a single enterprise he has been engaged in, i.e. his lifework.
To say his works assesses each piece as separate and not a contiguous body. So unless his publishing is eclectic I would avoid it.