I have a character with Rejuvenation Rank 3 and there is still no health regeneration in combat.
I tested by hiding near enemies where combat mode continued for at least a couple minutes before they gave up. My health bar did not move at all for those couple minutes.
V1.7.36.0
English (EN)
No
I guess I could start a new game, play through the tutorial, use the console to force my character to have Rejuvenation rank 3, then seek out a combat and let myself get injured, then run around and see if it works. I have not done this.