Youtube link (Lo-res version removed since obsolete)
Hi Res: http://www.youtube.com/watch?v=VIVFcOpxw4M
Sorry for the terrible resolution, I can work on getting it to higher resolution later, I'm also not sure why it loops and plays twice. You can see both of these monsters have an almost empty health bar however and recieve no damage when being attacked. They show no damage numbers but can be CC'd. They are not minions with Invulnerable Minion affix and do not have Shielding.
EDIT 2: I'm uploading a higher res version to youtube now, I'll post the link to the new version here soon as it's up so you can see the text clearer.
EDIT 3: For some reason the "higher res version" turns into Low res "240" once on Youtube. Will have it up atleast sometime in the future once youtube decides to behave.
EDIT 4: Okay finally have high resolution video uploaded.
To also add to this. If I ran past these guys so they were off my screen, then returned to them, they would have full HP and would take damage again. They would go from full health back down to just above 0 HP (likely 1 HP).