Technically, self-raging is taking advantage of a couple glitches in the game. But the glitches have been there for a very long time, and no devs were eager to fix them even when we had devs.
1) According to a dev a long time ago, shuffling rings is not supposed to lower your health. But a glitch in the ghi health bonus lowers your health bonus when you briefly only have 7 rings in your tray. Thus, healing wouldn't build rage because you wouldn't have any damage to heal.
2) Self-raging with armor buffs (Pot, Sphere, Teflon, or Rock) is less clear. I don't recall a dev ever saying, but something is glitched - I'm just not certain what the glitch is. Logically either using buffs should only build rage when they're replacing lower-rage versions of themselves (the way Rock does), or they should all build rage when they're replacing the same versions of themselves (the way Teflon, Pot, and Sphere do, but no other buff does), or else they should only build rage when the target doesn't have the buff at all. I don't know which behavior is best, but they should be consistent.