I don't think so. The Dreadnaught form is technically not a Devil Trigger, as far as I know... it's just a technique. ''A mysterious technique that transforms the body into a seemingly metallic shell impervious to enemy assault.'' - Devil May Cry Wikia.
The Majin form is Dante's last resort, like a power boost. But it is weird, because it seems to be a different Devil Trigger than his normal DT... so it could be that Majin form makes him fully demonic. It's possible that his normal DMC2 DT is mostly demonic but still also partly human.