I personally don't think the Bretonnian Men-At-Arms suit Empire at all, but that's just me. They'd be better if they had standard Empire style shields but their arms are part of their big tower shields so you kind of have to use them. A better option as above would be using Militia bodies with halberdier arms if you want something different or even tracking down a heap of random bits. You can use 6th Ed Spearmen bodies with Greatsword heads and halberds or you can try and find some 5th Ed multi-part plastics and update them with Greatsword/Archer/State Troop heads and/or Greatsword legs. You could use some archer bodies as well maybe for some different poses.
Unless of course the look you are after is Bretonnians fighting for the Empire, with feathers, in which case yeah, the Men-At-Arms with Empire heads and halberd tops will be fine.