Each writer definitely introduces his own ideas, some of which are extreme.
The Empire is chiefly the models made for it. R&F Empire units often carry shields.
Chronicles 2004 has the Cult of Ulric army list. There, Spearmen and Halberdiers have the normal shield option, but also Ulric specific units, Warriors of Ulric and Wolf-Kin, can have shields. I would say it doesn't get more definitive than that: shields are as much part of the Middenland/Ulric equipment as they are elsewhere in the Empire.
-Z