Unlikely, at least in the tradition conception of Nomads or any significant numbers.
Armageddon is a very hostile environment. You don't really want to be out travelleing the wastes and there's very little reason to. There's no animals to herd. There's no great trading routes.
Now it's possible there have been those who have become dissatisfied with hive life and cobbled together enough resources to leave, but they'd be few and far between. I also imagine it would be difficult to sustain these groups what with no doubt being considered rebels by Imperial Law. It's not like they can simply travel from hive to hive refuelling and trading- they'd be shot.
However Armageddon is now is the grip of the 3rd War. Hives have been sacked and destroyed, there are mass numbers of refugees ans scattered military groups. It's conceivable that splinters of these groups could come together and live in a nomadic faction, albeit temporarily. Roving bands of orks would kill them and Imperial forces conscript them.