No.
It'd be "(some) people on the forums are raging" or "a group of people is raging".
And bringing in other sentences just serves to muddy the argument. You'll do it so long until you're suddenly right with that new sentence. Doesn't affect the original one, so don't go down that road.
It's simple: "army" is singular, so you use the corresponding form of the verb,
"armies" would be plural and as such require the plural form. English is imprecise enough as it is, no point in making it moreso by making up grammar rules because you don't like/are too dumb to follow the given ones. /grammar nazi (Which I'm not. The only thing that gets on my nerves is mixing up "then" and "than".)