I've recently reread the Thrawn Trilogy(Heir to the Empire, Dark Force Rising, The Last Command) and found something interesting. In The Last Command, Niles Ferrier, a renowned ship thief, tips off an Imperial Garrison that Talon Karrde and other smugglers would be meeting on the planet Trogan. Despite direct orders from Thrawn, the commander of the garrison, Lieutenant Kosk, led a raid that resulted in the deaths of "four Imperial Stormtroopers and thirty-two Imperial Army Troops..."
Despite the Legends classification of the EU, the Thrawn Trilogy was the start of a new era of EU works. And while not considered canon in the film sense, it is/was very much considered canon among the works of the EU.
The graphic novel of The Last Command also clearly depicts Stormtroopers and the Army Troopers as two distinct types that Thrawn had spoken of, the black/dark grey clad troops with clamshell-like helmets fighting alongside the Iconic Stormtrooper. The link of the page in the graphic novel is here: http://starwars.wikia.com/wiki/Ambush_on_Trogan?file=Ambush_on_Trogan.jpg
I think this provides the greatest evidence that Stormtroopers exist alongside regular Army troops as a separate division. This may have been influenced by WEG but the fact that the concept of Army Troops exist in the novel in writing and as images in the graphic novel implies there was some approval given by Lucas or someone regarding it.
And another thing to ponder regarding the new Canon and the films. Since the Republic became the Empire, it stands to reason that a volunteer/conscript corps could also be created to serve as local garrisons to keep valuable combat Stormtroopers from getting complacent on guard duty (with the exception of Very Important Locations). It is very possible that this volunteer/conscripted corps could be called Imperial Army Troops.
I know you've already acknowledged it, but that doesn't make it any less true. All of the sources you mention are not canon. They're spin-off material in a time when Star Wars media wasn't being produced or properly organized.
Regarding local planetary armies, I talked about this myself earlier. There very likely are such things - it's an Empire, not a single state. Therefore subject systems will likely have local forces. These might be used on behalf of the Empire so there is that. They aren't really part of an "Imperial Army" though, at least no more than the British Indian Army I talked about earlier, was part of the British Army.